Advance Industries wastewater Mangement

Advance Industrial Wastewater Treatment

Wastewater Treatment

●Purpose:

   To manage water discharged from homes, businesses, and industries to reduce the threat of water pollution.

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What is pollution?

Pollution means:

  …changes in the physical, chemical and biological characteristics of air, land and water

  …harms for the human and other living species, and, 

  …degradation of the ecosystems

  ...the undesirable state of the natural environment beingcontaminated with harmful substances as a consequence of human activities

   For example, Water Pollution refers to contaminants in aquatic ecosystems (streams, lakes, etc) which render them unfit for a particular use.

Pollutants can reach:

•Air

•Water

•Solid waste

This module focuses on water pollution from industrial sources

Introduction:

We will start with an overview of treatment processes

1) Why do we treat water and wastewater?    

The main objectives of the conventional wastewater treatment processes are the reduction in biochemical oxygen demand, suspended solids and pathogenic organisms.

It also may be necessary to remove nutrients such as N and P, toxic components, non-biologically degradable compounds and dissolved solids.Removal of these materials are necessary for the simple reason that discharge to the environment will result in “damage” of some sort.

Of course the damage is a function of the type of pollutant discharged -- heavy metals = toxicity, organic matter = oxygen depletion, N or P- eutrophication, etc. In the case of water treatment the objective is to remove contaminants from the water which can result in health or aesthetic problems.

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2) What are the materials in water and wastewater that we must remove?

   There are a wide range of these pollutants (contaminants) ranging from municipal sewage to highly specific industrial wastes. The usual approach in discussing treatment schemes is to categorize pollutants into general classes so that a general class of treatment methods can be applied.

   Note that many pollutants fall into several categories. For example, some biodegradable organic matter (one category) is in the form of suspended solids (another category), so removal of SS sometimes results in the removal of organic matter. As an example consider the content of typical municipal wastewater as represented by its solids content.

3) To what level do we need to remove contaminants?

   The degree to which drinking water must be treated depends on the raw water quality and the desired quality of the finished water.   Similarly the degree of treatment of a wastewater depends on the quality of the raw waste and the required effluent quality.

For example wastewater treatment may require "secondary treatment" as shown here:

•BOD5 = 30 mg/L monthly average

•Suspended Solids = 30 mg/L monthly average

•pH (if there is industrial input) = 6 – 9 continuous

   Note that "secondary" standards are just the “basic” requirements. More stringent standards are placed on effluents which are discharged to potentially eutrophic lakes, etc. or whenever there is a known toxic contaminant in the wastewater (e.g. industrial discharges).

   For drinking water treatment the requirements are, of course, much more stringent with many more categories and lower contaminant limits.   Some examples are:

   Turbidity (a measure of suspended solids): less than 0.5 NTU in at least 95% of samples taken each month. 

   Lead: 0.005 mg/L

   Copper: 1.3 mg/L

   Total Coliform: no coliform detection in more than 5% of samples collected each month. 

4) How are these contaminants removed from water and wastewater?

   Contaminant removal is accomplished by a series of unit processes or unit operations. (In a strict sense "unit operation" is a physical treatment process and "unit process" is a chemical or biological process.  But, these terms are often used interchangeably). The system of integrated unit processes or unit processes used to treat a water or wastewater is called a treatment train.

   Now look at some typical treatment “trains”. Treatment “trains” are composed of a series of unit processes (or operations) each designed to remove a specific waste component or class of waste components. Arrangement and sizing of these unit processes is critical to their satisfactory and efficient operation. One of the objectives of this course is to develop an understanding of the unit processes, to know when to use a particular process, and how to size it to meet a certain performance level.

Treatment processes are usually divided into two trains: liquid train, and the solids (sludge) train. The reason for this is that we usually take a rather dilute waste and through a series of phase separation processes create a more concentrated waste (sludge). The sludge then has to be treated accordingly.

An example of a typical wastewater treatment  plant is:

Why should we minimize the use of water?

Water is such an important part of many manufacturing processes that we must consider Effluent Treatment as a part of the main process because of the great amount always involved.

Water is abstracted from aquifers and rivers, treated and supply to industries and homes for different uses; used water is supposed to be treated and discharged again into the rivers. Most of the times, this water returns to its natural environment but unfortunately, with a greater heat content or with some substances added. 

It is also important to minimize use of water because of several reasons:

➢Fresh water is often scarce. High costs involved operating effluent treatment plants.

➢Difficult to separate all the elements that pollute water.

Effluent Treatment Plant (ETP)

What is an ETP?

INFLUENT ETP TREATMENT

EFFLUENT

SLUDGE

• ETP (Effluent Treatment Plant) is a process design for treating the industrial waste water for its reuse or safe disposal to the environment. • Influent: Untreated industrial waste water. • Effluent: Treated industrial waste water. • Sludge: Solid part separated from waste water by ETP.

Need of ETP

• To clean industry effluent and recycle it for further use.

• To reduce the usage of fresh/potable water in Industries.

• To cut expenditure on water procurement.

• To meet the Standards for emission or discharge of environmental pollutants from various Industries set by the Government and avoid hefty penalties.

• To safeguard environment against pollution and contribute in sustainable development.

Design of ETP

The design and size of the ETP depends upon: • Quantity and quality of the industries discharge effluent.

• Land availability.

• Monetary considerations for construction, operation & maintenance.

• Area dimension depends on:  Quality of wastewater to be treated,  Flow rate  Type of biological treatment to be used .

• In case of less available land, CETP  (Common Effluent Treatment Plant) is preferred over ETP

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Treatment Levels & Mechanisms of ETP

• Treatment levels: 

 Preliminary 

 Primary 

 Secondary 

 Tertiary (or advanced)

• Treatment mechanisms: 

 Physical 

 Chemical 

 Biological

Preliminary Treatment level Purpose: 

Physical separation of big sized impurities like cloth, plastics, wood logs, paper, etc.

Common physical unit operations at Preliminary level are:

 Screening: A screen with openings of uniform size is used to remove large solids such as plastics, cloth etc. Generally maximum 10mm is used.

 Sedimentation: Physical water treatment process using gravity to remove suspended solids from water.

 Clarification: Used for separation of solids from fluids.

Primary Treatment Level 

Purpose: Removal of floating and settleable materials such as suspended solids and organic matter.

• Methods: Both physical and chemical methods are used in this treatment level.

• Chemical unit processes: 

 Chemical unit processes are always used with physical operations and may also be used with biological treatment processes.

 Chemical processes use the addition of chemicals to the wastewater to bring about changes in its quality. 

 Example: pH control, coagulation, chemical precipitation and oxidation.

Primary Treatment Level (cont…) 

pH Control:

 To adjust the pH in the treatment process to make wastewater pH neutral. 

 For acidic wastes (low pH): NaOH, Na2CO3, CaCO3or Ca(OH)2.  For alkali wastes (high pH): H2SO4, HCl. 

Chemical coagulation and Flocculation: • Coagulation refers to collecting the minute solid particles dispersed in a liquid into a larger mass. 

• Chemical coagulants like Al2(SO4)3 {also called alum} or Fe2(SO4)3 are added to wastewater to improve the attraction among fine particles so that they come together and form larger particles called  flocs. 

• A chemical flocculent  (usually a polyelectrolyte) enhances the flocculation process  by bringing   together  particles to form larger  flocs , which  settle  out  more  quickly.

• Flocculation is aided by gentle mixing which causes the particles to collide. 

Secondary Treatment Level 

Methods: Biological and chemical processes are involved in this level.

Biological unit process

 To remove, or reduce the concentration of organic and inorganic compounds. 

 Biological treatment process can take many forms but all are based around microorganisms, mainly bacteria.

Aerobic Processes

 Aerobic treatment processes take place in the presence of air (oxygen). 

 Utilizes those microorganisms (aerobes), which use molecular/free oxygen to assimilate organic impurities i.e. convert them in to carbon dioxide, water and biomass.

Anaerobic Processes 

 The anaerobic treatment processes take place in the absence of air (oxygen). 

 Utilizes microorganisms (anaerobes) which do not require air (molecular/free oxygen) to assimilate organic impurities. 

 The final products are methane and biomass.

Activated sludge process

Tertiary / Advanced Treatment

Purpose: Final cleaning process that improves wastewater quality before it is reused, recycled or discharged to the environment.

Mechanism: Removes remaining inorganic compounds, and substances, such as the nitrogen and phosphorus. Bacteria, viruses and parasites, which are harmful to public health, are also removed at this stage.

Methods: 

 Alum: Used to help remove additional phosphorus particles and group the remaining solids together for easy removal in the filters.

 Chlorine contact tank disinfects the tertiary treated wastewater by removing microorganisms in treated wastewater including bacteria, viruses and parasites.

 Remaining chlorine is removed by adding sodium bisulphate just before it's discharged.

ETP Plant Operation

1. Screen chamber: 

Remove relatively large solids to avoid abrasion of mechanical equipments and clogging of hydraulic system. 

2. Collection tank:

The collection tank collects the effluent water from the screening chamber,  stores and then pumps it to the equalization tank.

3. Equalization tank:  The effluents do not have similar concentrations at all the time; the pH will vary time to time.  Effluents are stored from 8 to 12 hours in the equalization tank resulting in a homogenous mixing of effluents and helping in neutralization.  It eliminates shock loading on the subsequent treatment system.  Continuous mixing also eliminates settling of solids within the equalization tank.  Reduces SS, TSS.

4. Flash mixer: 

Coagulants were added to the effluents: 1. Lime: (800-1000 ppm) To correct the pH upto 8-9 2. Alum: (200-300 ppm) To remove colour 3. Poly electrolyte: (0.2 ppm) To settle the suspended matters & reduce SS, TSS.

The addition of the above chemicals by efficient rapid mixing facilitates homogeneous combination of flocculates to produce microflocs. 

5. Clarriflocculator:

In the clarriflocculator the water is circulated continuously by the stirrer. 

 Overflowed water is taken out to the aeration tank. 

 The solid particles are settled down, and collected separately and dried; this reduces SS, TSS. 

 Flocculation provides slow mixing that leads to the formation of macro flocs, which then settles out in the clarifier zone. 

 The settled solids i.e. primary sludge are pumped into sludge drying beds.

6. Aeration tank:

 The water is passed like a thin film over the different arrangements like  staircase shape. 

 Dosing of Urea and DAP is done.  

 Water gets direct contact with the air to dissolve the oxygen into water. 

 BOD & COD values of water is reduced up to 90%.

7. Clarifier: 

 The clarifier collects the biological sludge. 

 The overflowed water is called as treated effluent and disposed out.

 The outlet water quality is checked to be within the accepted limit as delineated in the norms of the Bureau of Indian standards. 

 Through pipelines, the treated water is disposed into the environment river water, barren land, etc.

8. Sludge thickener: 

The inlet water consists of 60% water + 40% solids. 

The effluent is passed through the centrifuge. 

Due to centrifugal action, the solids and liquids are separated. 

The sludge thickener reduces the water content in the effluent to 40% water + 60% solids. 

 The effluent is then reprocessed and the sludge collected at the bottom.

9. Drying beds: 

Primary and secondary sludge is dried on the drying beds. 

FLOW CHART OF ETP

SCREENING

 Screening is the filtration process for the separation of coarse particles from influent.

 Stainless steel net with varying pore size can be utilized.

Screens are cleaned regularly to avoid clogging.

Equalization makes the waste water homogenous.

Retention time depends upon the capacity of treatment plant. (Generally 8-16 hours)

EQUALIZATION TANK

PH CORRECTION

In this tank pH of the influent is corrected to meet the standard.

Acid or alkali is added to the effluent to increase or decrease the pH.

Acid or alkali

Influent from equalization tank

pH correction

Influent of desired to pH disperse unit

DISPERSE UNIT

DISPERSE UNIT

( MIXING OF SLUDGE & WASTE)

Sludge from recycle tank

Influent from pH  correction tank Mixed influent & sludge to aeration

Disperse tank mixes the sludge coming from recycle tank with waste water for to proper aeration.

AERATION

• Function of aeration is oxidation by blowing air.

• Aerobic bacteria is used to stabilize and remove organic material presents in waste.

REACTION IN AERATION TANK:

SCHEMTIC DIAGRAM OF AERATION

Aeration Tank

Mixture of waste water & sludge

Aerobic bacteria

Discharge to sedimentation tank

ORGANIC MATTER + O2

CO2+ HO2 +  HEAT

BACTERIA

NUTRIENT

SEDIMENTATION TANK

In this tank sludge is settled down.

 Effluent is discharged from plant through a fish pond.

 Sludge is passed to the sludge thickening unit.

SLUDGE THICKENING UNIT

Here sludge is dried and discharged.

Partial amount of sludge is returned back to the aeration tank from thickening unit through recycle tank called return sludge tank and disperse tank.

Sludge Thickening vs. Dewatering 

Both are methods of solids concentration and volume reduction. Only the degree of volume reduction is different. Generally thickeners concentrate sludge at lower than 15% concentration, the dewatering units concentrate the sludge to higher than 15% concentration [3]. Thickened sludge still behaves as a liquid and can be pumped. However, the dewatered sludge generally behaves as a solid and can be trucked in most cases. 

Operation of a Thickener 

A thickener operates pretty much like a settling tank. The feed enters from the middle, are distributed radially, the settled sludge is collected from the underflow, the effluent exits over the weirs. 

In a continuously operated thickener, there are different zones of concentration. The topmost dear zone is free of solids and comprises the liquid that eventually escapes over the weirs. The next zone is called the feed zone although this zone does not necessarily have the same concentration of feed solids. This zone is characterized by a uniform solids concentration. Below the feed zone is a zone of increasing solids concentration (from feed zone concentration to underflow concentration). This zone is compaction zone. 

●  Pre-treatment

●  Preliminary treatment

●  Primary treatment

●  Secondary treatment

●  Sludge (biosolids) disposal

Wastewater Treatment

Wastewater Treatment

●  Pre-treatment

      - Occurs in business or industry prior to discharge

- Prevention of toxic chemicals or excess nutrients being discharged in wastewater

Wastewater Treatment

●Water discharged from homes, businesses, and industry enters sanitary sewers

●Water from rainwater on streets enters storm water sewers

●Combined sewers carry both sanitary wastes and storm water

Wastewater Treatment

●Water moves toward the wastewater plant primarily by gravity flow

●Lift stations pump water from low lying areas over hills 

Wastewater Treatment

Wastewater Treatment

●Preliminary Treatment

    - removes large objects and non-degradable materials

    - protects pumps and equipment from damage

    -  bar screen and grit chamber

Wastewater Treatment

●Bar Screen

   - catches large objects that have gotten into sewer system such as bricks, bottles, pieces of wood, etc.

Wastewater Treatment

●Grit Chamber 

   - removes rocks, gravel, broken glass, etc.

●Mesh Screen

   - removes diapers, combs, towels, plastic bags, syringes, etc.

Wastewater Treatment

●  Preliminary Treatment

Wastewater Treatment

●Measurement and sampling at the inlet structure

   -  a flow meter continuously records the volume of water entering the treatment plant

   - water samples are taken for determination of suspended solids and B.O.D.

Wastewater Treatment

●Suspended Solids – the quantity of solid materials floating in the water column

●B.O.D. = Biochemical Oxygen Demand

   - a measure of the amount of oxygen required to aerobically decompose organic matter in the water

Wastewater Treatment

●Measurements of Suspended Solids and B.O.D. indicate the effectiveness of treatment processes

●Both Suspended Solids and B.O.D. decrease as water moves through the wastewater treatment processes

Wastewater Treatment

●Primary Treatment

   -- a physical process

   -- wastewater flow is slowed down and suspended solids settle to the bottom by gravity

   -- the material that settles is called sludge or biosolids

Wastewater Treatment

●Primary Treatment

Wastewater Treatment

●Primary Treatment

Wastewater Treatment

●Primary Treatment

●Sludge from the primary sedimentation tanks is pumped to the sludge thickener.

   - more settling occurs to concentrate the sludge prior to disposal

Wastewater Treatment

Wastewater Treatment

●Primary treatment reduces the suspended solids and the B.O.D. of the wastewater.

●From the primary treatment tanks water is pumped to the trickling filter for secondary treatment.

●Secondary treatment will further reduce the suspended solids and B.O.D. of the wastewater.

Wastewater Treatment

●Secondary Treatment

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Wastewater Treatment

●Secondary Treatment

●Secondary treatment is a biological process

●Utilizes bacteria and algae to metabolize organic matter in the wastewater

●In Cape Girardeau secondary treatment occurs on the trickling filter

Wastewater Treatment

●Secondary Treatment

● the trickling filter does not “filter” the water

● water runs over a plastic media and organisms clinging to the media remove organic matter from the water

Wastewater Treatment

●From secondary treatment on the trickling filter water flows to the final clarifiers for further removal of sludge.

●The final clarifiers are another set of primary sedimentation tanks.

●From the final clarifiers the water is discharged back to the sea.

Wastewater Treatment

●The final clarifiers remove additional sludge and further reduce suspended solids and B.O.D.

Wastewater Treatment

●Disposal of Sludge or Biosolids

-- the sludge undergoes lime stabilization (pH is raised by addition of lime) to kill potential pathogens

-- the stabilized sludge is land applied by injection into agricultural fields

Wastewater Treatment

●Disposal of Sludge or Biosolids

-- in the past, Cape Girardeau disposed of the sludge by landfill or incineration

-- landfill disposal discontinued to the threat of leachate

-- incineration discontinued because of the ineffectiveness and cost 

Wastewater Treatment

●The final part of the field trip tour will be in the treatment plant lab.

Wastewater Treatment

●The wastewater plant lab conducts a number of measurements and tests on the water.

   

suspended solids        temperature

B.O.D.                nitrogen

pH                    phosphorus

Wastewater Treatment

●In addition to test performed at the wastewater lab, an off-site contract lab performs additional tests

heavy metals        priority pollutants

W.E.T (Whole Effluent Toxicity) tests

Wastewater Treatment Plant Occupational Health and Safety 

Exposure to toxic substances, pathogens and other hazardous materials can have a significant longterm impact on workers and their families with many workers experiencing lifelong disabilities. There are also risks of injury to the head, feet, hearing including crush injuries, lacerations.  This bulletin will primarily focus on exposure to chemicals and pathogens. 

I. Introduction 

Workers in the wastewater treatment sector are responsible for the day-to-day operation, maintenance, trouble-shooting and handling of special problems of municipal, industrial, and other wastewater treatment plants.  Occupations can include Level 1 WWR (Wastewater) Plant Operator, Level 2 WWR Plant Operator, Senior Operator, Water Resources Specialist, Maintenance Operator, etc in both municipal and private facilities

II. Injury Statistics 

In the United States (“U.S.”), this sector contains both recycling and waste management, therefore, the injury and fatality rates are combined.   

A 2009 U.S. Occupational Safety & Health Administration report put the incidence rate at 4.1 per 100 workers in the U.S.  Slips and trips are the number one cause of injury (TPO, 2013).  The most common physical injuries are strains and sprains to the back. 

There is little information about the long-term effects of exposure to chemicals and pathogens.  There is conflicting evidence regarding the development of cancer although pancreatic cancer appears to be higher in this sector1.  Generally, there is a much higher rate of injury generally than other occupations 

III. Who is Affected: 

Wastewater Treatment Plant Occupational Health and Safety Bulletin  

This sector includes workers involved with sewer inspection, maintenance work and sewage treatment plants operation.  Most workers are male between 35 and 55 years of age.  Workers may be employed in public or private facilities. 

IV. What are the Hazards: 

Workers in this sector are exposed to a variety of hazardous chemical and biological materials contained within the effluents and the reagents used in the water processing or generated during the water treatment.  

Chemical agents may cause acute poisoning, chemical accidents (e.g., skin burns, injury to the eyes, etc.) damage to the respiratory system, allergies, dermatitis, chronic diseases, etc.  Biological agents include pathogens such as bacteria, protozoa, viruses, helminths and fungi. 

There may be injuries by slips, trips and falls on wet floors; by falls into treatment ponds, pits, clarifiers or vats and by splashes of hazardous liquids; they may suffer cuts and pricks from sharp tools, contusions, etc.  

There is also exposure to hazards related to work in confined spaces (NIOSH, 2015).  

Strains and sprains are the most common types of injuries.  

The three primary types of exposure risks are: 

1. Biological  

There is a high potential for illnesses arising from contact with viruses, bacteria and other microorganisms in sewage.  

The most serious viral risk is hepatitis.  The most serious bacterial risk is tetanus.  

The main routes of exposure are hand-to-mouth contact.  Breathing in a suspension of particles (aerosols) is a less common means of exposure but may occur whenever sewage is agitated or aerosolized.  This occurs most commonly near incoming wastewater inlets and sludge treatment areas.  

2. Chemical  

Confined spaces containing sewage can sometimes be deficient in oxygen due to organic oxidation and displacement by carbon dioxide.  They can also contain flammable gases such as methane and toxic gases such as carbon monoxide and hydrogen sulphide.  Carbon monoxide, carbon dioxide, and other exhaust gases may sometimes be present due to a poorly located gasoline engine or generator exhausting into the confined space.  Chloroform is a common byproduct of disinfection. 

Wastewater Treatment Plant Occupational Health and Safety Bulletin 

3. Metals 

As per Brown (1997), metals are generally not air-stripped into the air in sufficient quantities to be significant (with the exception of mercury).  Therefore, they accumulate either in sludge or pass through into the receiving water.  Other possible hazards include asbestos and radioactive materials from medical facilities

The five main categories of pathogens are: 

o Bacteria

o Viruses 

o Protozoa 

o Helminths (parasitic worms) (CDC, 2002) 

o Fungi (CDC, 2002) 

Treatment processes do not eliminate the risk of exposure.  As per Brown (1997), the primary treatment process may remove 80 - 90% of Salmonella; 50% of Mycobacterium; and coliform removal varies from 27 - 96%.  The secondary treatment process removes from 50 - 90% of these pathogens.  Activated sludge has a low removal rate of 85 - 99% for pathogenic bacteria.  Waste solids do contain surviving pathogens.  Anaerobic digestion appears to reduce pathogens by 74% to 97% (Brown, 1997; CDC, 2002).  Tuberculosis, roundworms and certain enteric viruses appear highly resistant to treatment processes. 

The two primary routes of pathogen and chemical contact are: 

1. Inhalation  

This is the most common route for chemicals or pathogens to enter the body, usually via: 

o air-stripping from wastewater  o bubble aeration o workers working near weirs,  outfall and aerated tanks o dewatering processes o drying, compacting, incineration  o exposure to chemicals while removing debris from treatment plant equipment (Brown, 1997) 

The affected areas of the body initially include the nose, throat and upper respiratory tract.  Secondary areas are the eyes and lower respiratory tract (Brown, 1997).   

“Gas eye” due to hydrogen sulfide exposure is common2 in this sector. 

The most common specific pathogen exposures include (Lamfers, 2012; Brown, 1997): 

o Fecal streptococcus

o Mycobacterium tuberculosis  

o Gastroenteritis Enteroviruses (67 types), Rotaviruses, ("24-hour flu") 

o Infectious Hepatitis o Serum Hepatitis 

o Aseptic Meningitis

o Adenoviruses (31 types), Reoviruses, Coronavirus 

o Poliomyelitis

o Salmonellosis, Typhoid Fever 

o Shigellosis o Gastroenteritis (Escherichia coli) 

o Amoebic Dysentery, Ameobiasis

o Giardiasis o Meningoencephalitis

o Balantidiasis o Parasitic worms (roundworms, hook worms, tapeworms) 

o Fungi 

o Allergic asthma caused by exposure to sewer flies 

2. Skin Contact  

This is a route of entry for both chemicals and pathogens.  This includes being splashed in the mouth or on the skin.  Chemicals can be absorbed through the skin from contact with wastewater or sludge.  Disease organisms can enter the body through cuts, abrasions or needle sticks such as when removing screenings from a bar screen (Brown, 1997). 

V. Worker Education:   

Education about personal hygiene and safe work practices is extremely important to minimize contact with sewage and to prevent illnesses.  While the employer bears the primary responsibility, everyone in the workplace needs to exercise caution.  

Pre-planning, careful attention to personal hygiene and proper use of personal protective equipment (PPE) can greatly reduce the associated risks of exposure to sewage.  It is essential that information be provided to the worker on reducing the risks of exposure and injury.  Examples of worker practices include the following:  

o Avoid direct contact with sewage.  

Wastewater Treatment Plant Occupational Health and Safety Bulletin 

o Avoid aerosolizing sewage water or minimizing exposure time in areas where aerosolizing is occurring.  Make sure ventilation systems are functioning properly when working around areas where sewage may be aerosolized.  

o Thoroughly cleanse all exposed injuries with soap and water and keep them covered with a bandage (preferably waterproof) while at work.  Seek medication attention immediately after suffering cuts or penetrating injuries.  

o If a worker is suffering from a skin problem, they should see a physician before working with sewage.  

o Avoid touching the face, mouth, hands, eyes or nose with dirty hands or other items and avoid nail biting.   

o Thoroughly wash the hands and face with soap and water before eating, drinking or smoking.  

o Eat/smoke in designated areas away from sewage contamination.  These areas must be kept free from contamination by leaving any protective clothing and boots in a separate area, for example.  

o Use appropriate protective clothing at work (coveralls) and personal protective equipment (boots, gloves, plastic face shields) and, where required wearing respiratory protective equipment. 

o Remove personal protective clothing and footwear at the end of the shift and leave it at work.  

o Shower and change out of work clothes before leaving work.  

o Report damaged equipment.  

o Report all work-related symptoms to the employer and the physician. These may include:  

i. cramping stomach pains, diarrhea, vomiting  ii. yellowing of the skin  iii. symptoms of breathlessness, chest tightness and wheezing iv. redness and pain of the eyes  v. skin rash and/or pain  

Tests for disease exposure can include: 

skin tests for tuberculosis and fungal infections

i. ii. liver function tests for hepatitis 

iii. white blood cell (leukocyte) counts iv. urinalysis for fibrinogen degradation product (FDP) concentration 

Workers with these symptoms should see a physician.  Make sure that the physician is aware of conditions of work and potential exposures.  

VI. Employer Responsibilities Including Implementation of Control Measures.

What do the WorkSafe Act, Regulations and Policy say about air quality and hazardous substances exposure? 

A. Applicable RSIM II Policy items include #12.00, #25.10, #26.10, #26.22, and #29.10 as well as RSCM I Policy items from the pre-2002 / 2003 changes in legislation and RSCM I Policy where exposure occurred prior to 2002 / 2003. 

B. Applicable WorkSafe OHS Regulations3 include: 

o Section 3.10, which states in part that:  

Whenever a person observes what appears to be an unsafe or harmful condition or act the person must report it as soon as possible to a supervisor or to the employer, and the person receiving the report must investigate the reported unsafe condition or act and must ensure that any necessary corrective action is taken without delay.  

Part 3, Division 3 - General Duties of Employers, Workers and Others  o Part 3, Rights and Responsibilities

o Part 3, Section 4.13 – Risk Assessment 

o Part 3, Section 4.14 – Emergency Procedures 

o Part 3, Section 4.16 – Training o Part 4 - General Conditions 

o Part 4 - Working Alone or In Isolation 

o Part 4, Section 4.44 – Entrapment

o Part 4 - Occupational Environment Regulations 

o Part 4 - Indoor Air Quality 

o Part 5 - Chemical Agents and Biological Agents - Chemical Agents and Biological Agents - Definitions, Designation as Hazardous Substances, and General Information Requirement 

If a worker is or may be exposed to a chemical agent, or biological agent designated as a hazardous substance in section 5.1.1, which could cause an adverse health effect, the employer must ensure that 

(a) the identity of the chemical agent or biological agent, its possible effects on worker health and safety and any precautions required to protect the health and safety of the worker are clearly indicated by labels, SDSs, or other similar means, 

(b) the information required by paragraph (a) is clearly communicated to the worker, 

(c) written procedures are prepared and implemented to eliminate or minimize a risk of exposure to a chemical agent or biological agent by any route that could cause an adverse health effect, and to address emergency and cleanup procedures in the event of a spill or release of a chemical agent or biological agent, and 

(d) the supervisor and the worker are trained in and follow the measures required in this Part and Part 6 of this Regulation for the safe handling, use, storage and disposal of the chemical agent or biological agent, including emergency and spill cleanup procedures. 

What specific actions should employers take? These include the following (CDC, 2002; EPA, 2015):  

o Conduct Safety Tailboard sessions at the beginning of each shift. 

o Conduct a Risk Assessment.  This is a critical part of ensuring a safe work place and identifying risks.  See Figure 1 as an example of follow-up. 

o An employer must provide first aid services, supplies and equipment and provide a first aid room as per the applicable requirements of OHS legislation.  

Since pathogens are a natural part of sewage, the hazard cannot be eliminated.  A sitespecific assessment of the risk of worker’s exposure to the hazards of sewage must be completed.   

o Improve engineering controls such as ventilation. 

o Ensure that workers and management (and supervisors) understand risks through education on hazards, the importance of following safe work practices and the importance of hygiene measures.  Regular industry training may also be required per the industry association and legislation. 

o Ensure workers use appropriate PPE such as liquid-repellant coveralls and gloves, boots, goggles, respirators, and splash-proof eye/face shields.  If respirators are needed, a comprehensive program must include respirator fit testing and a respirator code of practice.  

Label piping. 

o Cover the primary clarifier weir area. 

o Ensure workers remove contaminated clothing after completion of a job (Lamfers, 2012). 

o Ensure workers shower at work and change into clean clothes (Lamfers, 2012). 

o Establish a proper system for purchase, inspection and maintenance of PPE.  

o Ensure areas for storage of clean and contaminated equipment and personal effects are segregated and separate from eating facilities, and have facilities readily available for decontamination of workers.  

o Develop and implement policies and procedures for post-exposure management of workers exposed to bio hazardous material. 

o Where feasible, substituting Class A biosolids could reduce the pathogen exposure risks during land application compared to applying Class B biosolids.  

o Monitor the source material coming from the wastewater treatment facility.  

o Check monitoring results to assure they meet specified Class B or Class A standards prior to land application operations.  

o Monitor stored biosolids prior to application to assure that the biosolids are properly stabilized and that unacceptable re-growth or cross-contamination from sub-standard material has not occurred.  

o Where local conditions permit, inject biosolids below the soil, or incorporate (thoroughly mix) into tilled soil.  

o On windy days, avoid spreading or disturbing dry biosolids (e.g., compost) that would create dust.  

o On windy days, avoid spreading biosolids by high-pressure spray to limit aerosolization.  

o Avoid unnecessary mechanical disturbance and contact with land-applied Class B biosolids during the period when public access is restricted.  

o Equip heavy equipment used at storage and application facilities with sealed positive pressure, air-conditioned cabs that contain filtered air recirculation units.  

VII. Basic Hygiene for Workers (CDC, 2002) 

In addition to the safety precautions for workers and employer, there are basic hygiene practices that can reduce the likelihood of exposure and injury.  These include: 

o Wash hands thoroughly with soap and water after contact with biosolids.  

o Avoid touching face, mouth, eyes, nose, genitalia, or open sores and cuts while working with biosolids.  

Wash hands before eating, drinking, smoking, and before and after using the bathroom.  

o Eat in designated areas away from biosolids handling activities.  

o Do not smoke while working with biosolids.  

o Use barriers between skin and surfaces exposed to biosolids. 

o Remove excess biosolids from footgear prior to entering a vehicle or a building. 

o Keep wounds covered with clean, dry bandages.  

o Flush eyes thoroughly, but gently, if biosolids contact eyes.  

o Change into clean work clothing on a daily basis and reserve footgear for use at work site or during biosolids transport.  

o Do not wear work clothes home or outside the work environment.  Use gloves to prevent skin abrasion. 

corrosion  problems in wastewater treatment

Corrosion damage in drinking water and sewage systems was estimated to be approximately $50 billion for 2009. Wastewater systems are often the most affected because of the extra impurities associated with waste. The resulting corrosion can cause failure of pipes and tanks as well as adding to the costs of removing impurities from the water.

Without corrosion inspections and maintenance, wastewater plants can see a reduction in electrical conductivity which can cause the plant to operate inefficiently or even fail. To avoid downtime, wastewater maintenance staff need to make sure they are regularly inspection of wastewater assets for the various types of corrosion and perform corrective and preventive maintenance.

Basic Corrosion Process at Wastewater Plants

Corrosion can come in several forms including:

•Electro-galvanic: better known as rust when oxygen molecules react with iron molecules.

•Electrolysis: caused by acids and bases in the water forming currents. Often the presence of hydrogen sulfide (smell of rotten eggs) is a sign of acidic buildup.

•Bacteria: Wastewater is filled with bacteria both added and inherent by its nature. Bacteria can eat away at iron and other metals.

•Chemical: Other chemicals and compounds can cause direct corrosion without water.

Wastewater treatment plants handle some of the most corrosive and aggressive liquids and solids known to process engineering. Pipes, tanks, pumps, and all the instrumentation that measures flow, level, pressure, temperature and other parameters are exposed to high concentrations of organic and inorganic compounds, sewage and industrial waste, corrosive chemicals, solids and microbiological organisms of all forms, as well as various gases.  Even the infrastructure is subject to corrosion – one Danish plant suffered considerable, and expensive, damage to an aluminium bridge structure.

While most process plants in other fields strive to remove all biological organisms and the threats of corrosion that they pose, the fundamental basis of any wastewater treatment operation is to cultivate bacteria and various other microbiological organisms at their maximum growth rate. A wastewater treatment plant consequently contains just about the greatest possible potential for steel pipe and tank damage caused by microbiologically influenced corrosion (MIC). 

The wide range of different wastewater components, in itself, makes it impossible to tackle the corrosion problems individually. Organic components of raw sewage are likely to include fats, greases, proteins, surfactants, oils, pesticides, phenols and many other aggressive compounds, some of which are likely to react with each other to create new substances. The inorganic components of raw sewage typically include heavy metals, nitrogen, phosphorus, sulphur, acids and a variety of strong alkalis – a veritable toxic soup.

Gases such as hydrogen sulphide, methane, ammonia, oxygen, carbon dioxide and nitrogen are commonly found dissolved in wastewater, among other corrosives.  Anaerobic decomposition of organic materials containing sulphur and nitrogen produces odorous compounds such as hydrogen sulphide, amines and volatile fatty acids.  Chlorine and ozone, disinfecting agents in the final phase of treatment, add further corrosion threats.

In addition, coagulants, flocculents, metal precipitants, emulsifiers, antifoaming agents, neutralizers, and odour control agents are added during wastewater processing.  A wastewater stream therefore contains enough corrosive compounds to damage just about any part of the process plant. 

The interaction of the primary components of sewage typically produces secondary chemicals and gases with even greater toxic and/or corrosive properties. Microorganisms cultivated at different stages throughout the wastewater stream produce a multitude of chemical and gaseous by-products - hydrogen sulphide (H2S) being a very common and particularly damaging by-product of MIC related bacteria. 

Sulphur-reducing bacteria (SRB), for example, reduce sulphates to sulphites in an anaerobic environment to produce hydrogen sulphide - H2S gas. Other aerobes, most commonly different strains of Thiobacillus, will oxidize the sulphur to sulphuric acid - producing pH values as low as 1.0, and attacking the concrete basins and most metals it comes in contact with.

Corrosion Protection for Water and Waste Water Treatment Plants

Corrosiveness Of Wastewater 

“Wastewater” in a municipal setting consists of  relatively weak solutions of non aggressive contaminant chemicals in “used” water.  The water is collected and conveyed to the treatment plant in pipes made of common materials, including cement mortar lined cast (ductile) iron, precast concrete, vitrifed clay and plastic, which includes a variety of thermoplastic or thermoset materials.   

The types and concentrations of contaminants in raw wastewater from domestic sources are well known - fats, oils, greases, soaps, organic matter, dirt, human waste, food waste, etc. - normally at total concentrations below 1000 ppm (0.1 per cent).   From a corrosion perspective, the sewage is no more corrosive than ordinary  “fresh” water, i.e., water that is neither acidic nor alkaline.  Wastewater is aerated in most parts of the wastewater system, at least where the biological reactions do not consume all the dissolved oxygen.  In areas where waste water is not aerated, it produces much more corrosive conditions for many materials. 

The most common chemical contaminants in domestic wastewater are chlorides, nitrogen compounds and a wide variety of organic compounds.  Sulfate and phosphate ions are present.  The pH of domestic wastewater typically is between 6 and 7, running slightly on the alkaline side of neutral where there is higher  use of soaps and household cleansing materials, most of which are mildly alkaline to increase their detergent effectiveness.  

Used water from manufacturing plants and factories - also called “trade waste”- can have a wider range of contaminants - some of which may significantly affect the corrosiveness of the wastewater.   However, most trade waste streams today must meet limits for contamination levels, especially for pH and heavy metal ions, set by the treatment plant that accepts them. 

Today, industrial contributors of wastewater are required to provide pH control and chemical pretreatment of their waste water for the removal of heavy metal ions.  However if not properly managed, metals removal and pH control can affect the corrosivity and toxicity of the wastewater in municipal collection and treatment systems. 

Microbiological Considerations 

Sewage and other wastewaters contain significant levels of biological and organic materials,  including many bacteria that remain active in the waste streams.  From a corrosion point of view, the most important types of bacteria are those that metabolize sulfur compounds because this microbiological activity can produce acidic chemicals that are corrosive to concrete and steel or iron.  Some bacteria also oxidize ferrous ions to ferric ions, which makes the local environment more corrosive to carbon steel

bacteria in wastewater streams and systems are the genus thiobacillus.  These organisms grow best at 25-35°C.  They are able to oxidize sulfide, elemental S, thiosulfate, and polythionite.  

The genus Thiobacillus can be broken into two groups. The first are those that grow only at neutral pH values. These are responsible for the conversion of elemental sulfur into sulfuric acid.  Another group grows at lower pH values and can utilize Fe2+ as an electron donor.   

In this second group, Thiobacillus thiooxidans has a much more acidic growth range. It grows best between 2 to 5 and is also strictly aerobic.  Thiobacillus intermedius is most active in a pH range of 3 to 7, gets its electrons from (i.e., oxidizes) thiosulfate ions (S2O32-), and is stimulated by the presence of organic matter.  Thiobacillusferrooxidans is strictly aerobic and it has a pH growth range of 1.5 to 5.  It can oxidize Fe2+ to Fe3+. 

The production of sulfuric acid is the major problem related to Thiobacillus.  Formation of H2SO4 in municipal wastewater systems is a two-stage process: bacteria produce sulfide ions and hydrogen sulfide, which are metabolized by other bacteria to produce oxidized sulfur species that react with water to produce sulfuric acid. 

Bio-Generation Of Sulfides

Domestic septic sewage contains an ample supply of sulfate ions (SO42-).  Within the slime layers that form on sewer piping and other sewage handling surfaces, sulfate reducing bacteria (SRB) also exist.  SRB are anaerobic and are dormant until the slime layer is thick enough to cut off the dissolved oxygen and produce anaerobic conditions.  Once this occurs, usually within 1 or 2 weeks, depending upon local conditions, the SRB metabolize the sulfate ions – reducing them to sulfide ions (S2-).  The sulfide ions react with hydrogen ions in the wastewater to form hydrosulfide, also called the bisulfide ion (HS-).  HS- ions react with water to produce hydrogen sulfide (H2S) in the dissolved form. 

Bisulfide ions acidify the water, increasing the concentration of hydrogen ions.  This speeds up formation of HS- ions and of H2S gas.  Dissolved H2S gas comes out of solution at regions of turbulence, but more gas forms to replace it.  H2S coming out of solution and entering the atmosphere causes the familiar “rotten egg” odor.   

Bio-Generation Of Sulfuric Acid Sulfur-oxidizing bacteria (SOB) colonize on wet surfaces with pH above about 9.5 and if oxygen is present.  Aerobic SOB are especially active in a nutrient rich, scum layer generally found just above the waterline.  SOB uses dissolved oxygen to metabolize H2S and other sulfides to sulfuric acid (H2SO4). As noted earlier, the acid-generating SOB are mainly members of the Thiobacillus genus.  Many species of Thiobacillus are involved in the production of sulfuric acid in sewer systems.  Different types of thiobacillus bacteria thrive under different conditions, including pH.  If one type can no longer survive because conditions become too acidic, another will take over.  This process continues to very acidic pH levels around 1.0, provided the bacteria also have enough nutrient, H2S and dissolved oxygen to keep conditions aerobic.  

Modern Conditions Are More Severe Hydrogen sulfide (H2S) is always present in municipal wastewaters and has always caused a certain amount of acidic attack of portland cement concrete in WWT systems. Through the 1970’s, H2S concentrations up to 15 ppm, but averaging 2 to 10 ppm, were commonplace in sewer pipe crowns and headspaces in conveyance/treatment structures.  The acidic conditions from these levels caused only gradual concrete attack, via loss of cement paste.  When H2S concentrations reach 50 ppm during periods of low sewer flow and elevated ambient temperature, such as during summer droughts, concrete attack can proceed at up to 0.5 in./yr.    

One proposed reason for these moderate H2S concentrations was the presence of heavy metals ions, which reduced aqueous sulfide levels in the wastewater by their toxic effect on the sulfide-generating bacteria.  After the Clean Water Act of 1980 dramatically lowered the allowable levels of heavy metal ions in waste streams discharged by industrial plants, the  bacteria responsible for aqueous sulfide production in wastewater systems proliferated.  This resulted in more sulfide-related corrosion (and odor) problems in WWTPs in the last 25 years

Concrete Deterioration and Concrete Fundamentals  

Uncoated concrete pipe and structures in wastewater service deteriorate, sometimes quickly, from exposure to a variety of chemical and physical conditions.  Design and selection of appropriate protection or remedial measures for concrete in WWTPs requires an understanding of the thenature of concrete and of the chemical and physical conditions that cause concrete to deteriorate.  

Concrete is a composite material made from sand, rock and cement. The cement is a mixture of various minerals which, when mixed with water, hydrate and rapidly become a hard binder that locks the sand and rock into a solid mass.  

Chemical Deterioration  

Rates of deterioration of the intrinsically alkaline concrete due to chemical attack in a WTTP depend both on the nature of the service environment and on the permeability of the concrete.  The natural alkalinity of concrete makes it highly vulnerable to acid attack, but generally resistant to neutral and alkaline environments.  The permeability of the concrete - related strongly to the w/c - governs how rapidly harmful agents move into or through the hardened concrete, which in turn affects how rapidly the reinforcing steel in the concrete is reached by corrosive agents including water, that corrode the steel. 

The four primary mechanisms of chemical deterioration of concrete in a WWTP are:  

1. Acid attack (by biogenic acids).

2. Carbonation 

3. Chloride-related deterioration

4. Sulfate attack 

Each mechanism and common preventive measures are discussed in more detail below. 

Acid Attack 

Acids react with concrete in a standard, acid-base neutralization reaction.  The most common acid environment in WTTP is the sulfuric acid formed by bacterial action and from reaction of hydrogen sulfide, water, and air.  The rate of neutralization depends on the initial acid concentration and on the type of acid.  

The hardened cement paste in concrete is very alkaline, usually starting out with a pH above 12.5.  When exposed to acids or acid solutions, the cement reacts with the acid to produce soluble salts.  These are mostly calcium salts because the hydrated cement is about 25% calcium hydroxide. Acid attack dissolves the cement phase of the concrete away, exposing the less soluble coarse aggregate materials.   

Preventing Acid Attack 

Resistance of regular concrete to acid attack can be improved by with dense, low permeability concrete, i.e, mixes with water:cement ratios below 0.40, and by minimizing cracking of the cured concrete mass through use of proper design, curing and placement practices.  Resistance to sulfuric acids is marginally improved by using sulfate-resisting cement. Use of micro-silica and silica fume in concrete can improve acid resistance by reducing permeability and by making the cement paste less readily soluble.  However, concrete made with portland cement is generally subject to acid attack by solutions with a pH less than 5.0.  Solutions with pH values below 4 will attack concrete made with any type of portland cement.   Mortars based on calcium aluminum silicates (such as Lumnite) can be used for environments with pH below 5.5, but calcium aluminum silicate cement is rapidly attacked if the pH goes above 8, especially if sodium or potassium hydroxides are present. 

Preventing Carbonation 

Coatings and sealers are effective in reducing atmospheric and liquid phase carbonation of existing concrete structures.  Susceptibility to surface carbonation can be reduced by getting good consolidation, avoiding poor finishing techniques that cause a wetter surface layer and by wet curing for 7 days.  Carbonation does not significantly affect low permeability concrete for many years. 

Chloride-Related Deterioration 

When the wet concrete is placed around bare, carbon steel reinforcing bars, a corrosion reaction between the steel and the alkaline cement paste produces a tightly adherent, protective, oxide film on the steel surface.  This “passive” film is stable at pHs higher than 11 and prevents corrosion of the steel as long as the film is not damaged or removed. 

Preventing Chloride-Related Deterioration 

Because chlorides in concrete are not harmful unless water and oxygen also are present, chloride-related deterioration can by prevented by eliminating any of the three critical elements of the corrosion mechanism.  The simplest approach is usually to prevent water access through the concrete to the steel.   

This can be done for new concrete by minimizing both intrinsic permeability and subsequent cracking of the cured concrete.  The former normally involves specifying the lowest possible water:cement (ratio) in the mix design and using pozzolanic admixtures such as silica fume (or micro-silica) to significantly improve concrete density and reduce permeability.