Regulations and permits require treating industrial waste streams for defined industries before the water is discharged 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 U.S. Environmental Protection Agency (EPA) established categorical pretreatment standards for at least 35 categories of industrial dischargers. They encompass 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.
Wastewater has been viewed as a disposable product for most industries. However, recycling and reuse within the facility and a move toward no discharge have grown significantly.
Characteristics of waste
Technologies for treating 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.
Pretreatment technologies for biodegradable organics are similar to those used for conventional sewage treatment. For example, activated sludge and trickling filters provide aerobic and anerobic processes. Activated sludge, an aerobic medium, involves injecting 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.
Many industrial organic chemicals are slowly biodegraded or are not biodegradable or toxic to microbial media, so physical processes serve as the primary treatment. These wastes include pharmaceuticals, pesticides, solvents, paints and other synthetic organic chemicals.
Many metals and their salts are toxic to the environment or to animals and humans, and they cannot easily be removed by publicly owned treatment works. 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.
Food and beverage
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.
Wastewaters with significant biochemical oxygen demand and total suspended solids could overwhelm biological treatment processes when a public facility is receiving peak loads. 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.
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 and technical editor of Water Technology.