Q: What are the wastewater treatment requirements and the technologies appropriate for designated commercial and industrial wastewaters?
A: Regulations and permits require treating commercial and industrial waste streams before discharge to the sewer system. The type of waste being produced and the potential disruption of municipal wastewater treatment systems determine the specific goals and treatment.
The January Professor POU/POE discussed municipal wastewater treatment facilities, commonly called publicly owned treatment works (POTWs), and domestic treatment systems. This article reviews pretreatment requirements and technologies intended to protect POTWs from discharges to sewers of pollutant types and levels that could interfere with the functioning and performance of POTWs. In addition, they are intended to improve opportunities to recycle and reclaim municipal and industrial wastewaters and sludges.
The Federal Water Pollution Control Act, known as the Clean Water Act (CWA), was passed in 1972 to maintain and improve the quality of ambient waters. Its goal was to eliminate the introduction of pollutants into navigable waters and to achieve fishable and swimmable water quality. The National Pollutant Discharge Elimination System (NPDES) and its permit programs establish requirements for point source direct dischargers to the water environment. The National Pretreatment Program, a component of NPDES, requires indirect industrial and commercial waste dischargers, or those that discharge wastewater to a POTW, to obtain permits that specify the effluent quality to be obtained by pretreatment or other controls before discharge to the sewer.
POTWs are designed to treat domestic sewage made up, predominantly, of biodegradable household and commercial waste. These conventional pollutants include: biochemical oxygen demand, total suspended solids, fecal coliforms, pH, oil and grease. Many pollutants are not amenable to biological treatment and can pass through untreated. Even if the POTW can remove toxic pollutants, they will be concentrated in biosolids or sludges that could be applied as fertilizer or soil conditioner for food crops, parks or golf courses.
The pretreatment controls are intended to prevent interference or disruption of the POTW, so its discharges and sludges will not damage the receiving waters or environment. The regulations require POTWs that treat more than 5 million gallons per day and smaller facilities that receive wastewater from defined industrial users to establish local pretreatment programs that will enforce national and local requirements. Approximately 1,600 POTWs have established pretreatment programs that include 23,000 significant industrial users.
The U.S. Environmental Protection Agency (EPA) established categorical pretreatment standards for at least 35 categories of industrial dischargers. They can include requirements for existing sources as well as standards for new sources. Examples include: aluminum forming, battery manufacturing, concentrated animal feeding operations, electroplating, ink formulating, inorganic chemicals manufacturing, oil and gas extraction, foods, organic chemicals and plastics, pesticide chemicals, pharmaceutical manufacturing, pulp and paper, paperboard, soap, and detergent manufacturing.
In addition, the industrial effluent guidelines describe treatments and performance expectations for 58 categories of direct dischargers, and several more are in development that are accessible in the Code of Federal Regulations at 40 CFR 405-499. The treatment technologies described in the guidelines also apply to the pretreatment for indirect dischargers. The standards are based on the performance of the treatment and control technologies and not on risk or impacts upon receiving waters. The discharge permits are usually numerical concentrations intended to protect the receiving waters.
Wastewater is a disposable product for most industries, but significant movement has grown in recycling and reuse within the facility or toward no discharge. Depending on the industrial process, the waste can be recycled, reused, released to a sewer or to a surface water, combusted, vitrified, or deep-well injected. Appropriate regulations and permits cover these options.
Technologies for waste streams are selected based on the chemical and physical characteristics of the waste. These include high salinity, solids, pH range, high biodegradability, toxicity, hydrophobicity, inorganic chemicals and synthetic organic chemicals/pharmaceuticals.
Wastes with excessively high salinity will require processes that remove dissolved ions. These wastes could include: reverse osmosis reject water, pulp and paper processing water, waste streams from food and beverage processing, cooling tower water, natural gas and oil extraction including hydraulic fracturing fluids, and chloralkali wastes. Brine treatments are designed to produce varying degrees of purified water and to minimize the residuals that must be disposed. The wastewater treatment processes include: evaporation/distillation systems, membrane separation processes, electrodialysis, salts concentrators and ion exchange.
Biodegradable organic materials
Pretreatment technologies for biodegradable organics are similar to those used for conventional sewage treatment in POTWs. For example, activated sludge and trickling filters provide aerobic and anerobic processes. Activated sludge is an aerobic medium and involves the injection of air or oxygen to facilitate oxidation by the microorganisms that metabolize and decompose many of the carbon containing chemicals.
In trickling filters, an older form of waste treatment, wastewater passes through a bed of inert rock or other large granular material, and the filter medium surface provides sites for microbial proliferation. As the wastewater percolates through the material, the organics can adhere to the surfaces where microbial activity occurs. The treatment is usually aerobic, but anerobic zones will also develop. Generally, activated sludge processes produce a consistently higher quality of effluent water than trickling filters.
Less or nonbiodegradable organic chemicals
Many industrial organic chemicals are slowly biodegraded or are not biodegradable or toxic to microbial media, so physical processes serve as the primary treatment. Some of these wastes include pharmaceuticals, pesticides, solvents, paints and other synthetic organic chemicals. Treatment processes include physical separation of non-water soluble chemicals, adsorption on activated carbon, combustion, distillation and advanced oxidation.
Acids and bases
Reactions with the opposite reagent neutralize strongly acidic and basic chemicals at extremes of pH. Bases are neutralized by acids such as hydrochloric acid, and acids are usually neutralized by caustic bases (sodium hydroxide) or limestone/lime bases (calcium carbonate or calcium oxide).
Many metals and their salts are toxic to the environment or to animals and humans, and they cannot easily be removed by POTWs. Pretreatments involving precipitation, separation and concentration followed by disposal in landfills are typical if recovery and recycling are not feasible.
Oils and grease
Both natural and synthetic oils and greases are mostly not miscible with water. They will float on the surface and be skimmed and reprocessed, biodegraded or disposed, perhaps by combustion.
Agricultural and food operations are distinct from most other industrial categories because their waste products are generally biodegradable and nontoxic. However, the industry is often seasonal and has significant production peaks. Agricultural product waste streams that involve animal slaughter sources can contain blood, feces and other fluids. The waste streams can also have antibiotics, hormones and pesticides. Categories of food production covered by effluent guidelines include:
- Canned and preserved fruit and vegetable processing
- Canned and preserved seafood
- Dairy products processing
- Grain mills manufacturing
- Meat and poultry products
- Sugar processing
Looking at pretreatment concerns, wastewaters with significant biochemical oxygen demand (BOD) and total suspended solids (TSS) could overwhelm the biological treatment processes when a POTW is receiving peak loads. Excessive nitrogen and phosphorous nutrient loads are also subject to controls. Discharges to sewers could be prohibited for some processes, given a production-based daily maximum and/or 30-day average limitations, or they may be concentration-based. Toxic chemicals and pathogens are not generally a significant concern, except potentially in meat and poultry processing that often uses aerated lagoons to reduce organic content before release or reuse. Recycling is permitted within a specific process stage.
Treating industrial waste is essential to protect public health and the environment. Technology- and industry-based effluent guidelines and permits control direct discharges to the environment. Pretreatment requirements and permits for indirect discharges to sewage treatment plants protect POTWs from major treatment disruptions from wastes that would cause the water discharges to exceed permit requirements. Some industrial wastes can be recovered and recycled, but others require mitigating treatment and disposal. The treatment processes, which depend on the waste characteristics, include physical and biological treatments as well as specific chemical separations.
Dr. Joe Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the EPA Drinking Water Standards Division.