Texas Basic Waste Water Operations Ch#04 Domestic Waste Pretreatment

Domestic wastewater is not uniform in content. It is a mixture of wastes discharged from many sources. The content of wastewater depends on the amount and source of the waste.

Some waste is not treated in a domestic waste treatment plant because it can harm the biological process or contaminate the sludge. An operator should know which wastes must be pretreated or prohibited from entering a domestic wastewater treatment facility.

Sources of wastewater include the following: • Domestic (homes and businesses) • Inflow and infiltration (stormwater, shallow water tables) • Commercial (restaurants, car washes, gas stations, laundries) • Food processing (canneries, slaughter houses, breweries) • Agricultural (dairies, cotton gins, feed lots) • Industrial (chemical plants, paper mills, metal plating, refineries)

Domestic wastewater is a small amount of waste carried by a large amount of water. By weight, domestic wastewater is about 99.9% water and 0.1% solids.

Flow from domestic sources averages about 100 gallons/day per person served. The flow rate changes throughout the day in a repeating pattern. During dry weather, peak flow is twice the average flow, and minimum flow is about half the average.

Inflow is stormwater that enters a collection system through openings such as broken house line cleanouts and open manholes. Infiltration is water that enters through cracked pipe and brick manhole walls. Inflow and infiltration (I & I) creates a flow 5–10 times higher than the daily average. The result is bypassing, plant washout, poor treatment, and permit violation. I & I is difficult and expensive to correct. Sometimes it is cheaper to build a flow equalization basin at the treatment plant.

Inflow is stormwater that enters a collection system through openings such as broken house line cleanouts and open manholes. Infiltration is water that enters through cracked pipe and brick manhole walls. Inflow and infiltration (I & I) creates a flow 5–10 times higher than the daily average. The result is bypassing, plant washout, poor treatment, and permit violation. I & I is difficult and expensive to correct. Sometimes it is cheaper to build a flow equalization basin at the treatment plant.

Inflow is stormwater that enters a collection system through openings such as broken house line cleanouts and open manholes. Infiltration is water that enters through cracked pipe and brick manhole walls. Inflow and infiltration (I & I) creates a flow 5–10 times higher than the daily average. The result is bypassing, plant washout, poor treatment, and permit violation. I & I is difficult and expensive to correct. Sometimes it is cheaper to build a flow equalization basin at the treatment plant.

Inflow is stormwater that enters a collection system through openings such as broken house line cleanouts and open manholes. Infiltration is water that enters through cracked pipe and brick manhole walls. Inflow and infiltration (I & I) creates a flow 5–10 times higher than the daily average. The result is bypassing, plant washout, poor treatment, and permit violation. I & I is difficult and expensive to correct. Sometimes it is cheaper to build a flow equalization basin at the treatment plant.

Food processing discharges large amounts of organic material. Food processing waste causes blockages, odor, plant overload, and plant nutrient imbalance.

During wash down at stockyards, feed pens, dairies, and grain elevators, excessive solids and organics can enter the wastewater system. This causes stoppages and organic overload. Pesticides and herbicides are toxic to the plant biological system. Chemicals may enter the plant as waste or by stormwater I & I.

Refineries, paper mills, and metal platers all contribute shock loads to the treatment plant. These industries produce acid or alkali wastes, which cause corrosion, damage pumps, and disrupt treatment. The wastes are hazardous to equipment and personnel. It is necessary to neutralize these wastes at the source when the pH is lower than 5 or greater than 10. Acids, bases, or buffers should be mixed with the waste to bring the pH close to 7.0 (neutral).

The EPA requires 58 categorical industries to pretreat wastes before discharging to a Publicly Owned Treatment Works (POTW). NOTE: yes i know TEEX symbol speaks WAY too much and that this is an asinine question. i remember this one because to me it reads a bit like "pot(able) w(ater)" and the others are gibberish. the abbreviation POTW for publicly owned treatment works is something you will see over and over again though.

Monitoring industrial waste prevents the following: • Worker exposure to chemical hazards (most important) • Interference with treatment • Sludge contamination • Pollutants in effluent • Explosions or fires

Federal regulations require an industrial waste control program when flow exceeds 5 million gallons per day (MGD) or an industrial waste is regulated by federal standards (CFR, Title 40).

Toxins discharged to biological treatment may have an acute or chronic effect. Acute toxicity causes rapid die-off of treatment organisms. The problem must be corrected to avoid a plant upset or permit violation. Chronic toxicity inactivates microorganisms over days or months. If the toxins accumulate, the treatment process will fail.

Permittees must prohibit or restrict discharges that damage the treatment system. The TCEQ has no specific pretreatment standards, but EPA requires waste with characteristics listed below to be pretreated with best available technology before discharging to a POTW.

Characteristics of restricted discharge include the following: • Wastewater hot enough to damage pipe joints (150°F) or harm biological processes (104°F) • Fire hazards • Corrosive materials • Contents that will obstruct flow • Materials that will create a shock load • Toxic materials • Materials contaminated with radiation

Pretreatment processes vary with industry, but often include the following: • Spill control, rinse reduction, and recycling • Oxidation of chromium, sulfides, or cyanide • Biological stabilization • Waste segregation • pH control • Sludge removal • Metal removal • Flow equalization • Oil removal