Effects of Industrial Wastewater

Some of the effects of industrial wastewater discharges on collection and treatment systems were discussed briefly before. This section will describe in more details how industrial wastewaters can affect the operation and performance of both the IWTS and the POTW, and how direct discharges to the environment could affect receiving waters.
If an industrial wastestream is discharged to an IWTS which was not designed to handle it, the discharge may cause serious problems. It could interfere with the IWTS processes and/or pass through untreated to the POTW sewer. Similar effects may occur at the POTW and result in a violation of the discharge permit or prevent the reuse or recycle of water. The untreated industrial discharge could contaminate the industrial wastewater sludge or cause an air emission problem. It potentially could affect maintenance or production personnel working in or around the industrial sewer or treatment system through the generation of a toxic gas.
The seriousness of the effect will depend on the characteristics of the industrial wastestreams, the size and design of the IWTS, and the standards for discharge, recycle or disposal of wastewater, sludge or air emissions. Accordingly, the effects of discharging the industrial effluent to the POTW or the environment will depend on the characteristics of the effluent, the type and size of the POTW system, and their standards for sludge and wastewater disposal or reuse. Waste characteristics such as temperature, pH, odor, toxicity, concentration, and flow must be evaluated to determine their acceptability to the IWTS. Similarly, understanding these characteristics of the IWTS effluent will also enable to predict the effect the effluent may have on the POTW system.
The effects of industrial waste discharges are not always negative; some beneficial effects also occur. For example, in a short POTW collection system, such as a small treatment system discharging to a trout stream, a continuous discharge of boiler blowdown from a large power plant can be cause for concern. High temperature discharges to sewers can accelerate (1) biological degradation, (2) slime growths, (3) odor production from anaerobic decomposition, and (4) corrosion of concrete pipe and metal sewer appurtenances. The high temperature wastewater can cause a bacterial population shift in the secondary treatment causing floating sludge and reduced BOD removal efficiency. This in turn would endanger the treatment plant’s ability to meet its discharge permit limits. The high temperature wastewater may also cause the plant to exceed its temperature standards to the trout stream.
On the other hand, the high temperature wastewater discharge from a power plant in a larger conveyance and treatment system located in a colder climate may, in fact, enhance the POTW secondary treatment processes removal efficiencies by keeping the wastewater temperature above 65 F (18 °C) all year. When evaluating an industrial wastestream, it is necessary to understand the specific characteristics of the waste and how they may affect each portion of the IWTS and in turn how the effluent will affect the POTW’s conveyance, treatment, disposal, and reuse facilities.

1-1 Effects on the collection system

The IWTS collection system is designed and built to transport the individual and combined industrial wastestreams. If the collection system is not designed, built or operated correctly or if there is a spill, leak or accidental discharge of materials, the industrial discharges by themselves or in combination with other industrial wastewater can cause plugging, odors, erosion, corrosion, explosions, and numerous other problems. The good news, however, is that some industrial discharges contain substances that have a positive effect on the collection system, which may mitigate (lessen) the effect of another industrial wastewater. The beneficial effects could include in-line neutralization. Large flows may produce scouring velocities in low-flow sewers or dilute a concentrated spill enough to produce a treatable waste within the capabilities of the IWTS.

1-1-1 Hydraulic capacity problems

Hydraulic overload problems can occur if a large slug of wastewater or a continuous flow is discharged to the industrial sewer. The cause of a slug discharge may be a tank rupture or water line break. The cause of a continuous large flow may be a broken valve or one left open by mistake. The result in either case may be a sewer backup or pump station overflow. The smaller the capacity of the sewer or system, and the larger the contribution by the individual wastestream, the more likely it is this problem will occur. The solution may be to require flow restrictors on water valves or tank level switches to alarm high or low levels. If the condition regularly exists, for example, because of the introduction of a new manufacturing process that discharges a slug, equalization of the discharge may be necessary to store the effluent for off-peak hour discharge. A hydraulic overload condition may also occur if similar manufacturing processes discharge at the same time. For example, in a food processing industry there may be two sections of the plant that clean tanks, reactors, or cooking pots at virtually the same time. While the discharge from one manufacturing line may not cause a problem, the similar discharge schedule from another line will combine the wastewater flows and cause a hydraulic overload condition. Possible solutions include equalization of flow at the IWTS or at the manufacturing process and scheduling production and cleanup so that both lines are not cleaning at the same time.

1-1-2 Plugging

If the discharge from a manufacturing process contains large amounts of fibrous or stringy materials, heavy solids, adhesives, or grease, plugging of the sewer system may result. Plugging may occur just downstream of the discharge or in the pumping station. Fibrous or stringy materials get caught on rough surfaces and soon build up by entangling more solids. These types of materials can also wind themselves around pump impellers or shafts causing the pump to fail. If problems are occurring, it may be an indication of a problem with the manufacturing process or that the waste should have been pretreated prior to discharge. Review the manufacturing process to determine if changes in the process or disposal of wastes are required or if the sewer needs to be enlarged to accommodate the materials. Heavy solids such as sand, ceramic or porcelain solids, or grindings can build up in a sewer or pump station wet well and reduce its hydraulic capacity. Solids that are not removed by pretreatment at the process may be discharged during peak wastewater flows during the day and may settle in pump station wet wells or oversized sewers downstream of the actual point of discharge when the flow subsides. The solids then have an opportunity to compact and may not become resuspended when the flow in the sewer returns to its peak flow. This cycle of transporting the solids to a section of the collection system to settle, build up, and compact will eventually cause a restriction. A complete blockage may also occur if large objects are released to the sewer. Rags, tools, rejected food products, and discarded by-products may accidentally be released to the sewer due to operator carelessness or equipment malfunction. Because of their size, they can easily become wedged or entangled with other waste material and completely block the sewer or lift station pump.

1-1-3 Odors

Examples of industrial discharges that can be odorous are those from petroleum refining, petrochemical manufacturing, and food processing. Generally, the odors are produced from a compound containing sulfur, such as mercaptants or hydrogen sulfide. These compounds in air are detectable in the parts-per-billion range (by volume) and can cause complaints from residents and other industries. While the problem is airborne, the actual cause originates in the industrial discharge. It is even more common to find this problem in the discharge to the POTW system. The first solution may be to change the manufacturing process. Sour water, which is wastewater containing high concentrations of sulfide from the petroleum refining industry, can be stripped with steam and reduced to elemental sulfur using the Klaus process. This process and other similar recovery processes have reduced the odor pollution problem while producing a saleable by-product (sulfur). Another solution may be to oxidize the offending components prior to discharge using air, hydrogen peroxide, or chlorine; or not discharge them at all. The wastewater produced during the etherification reaction to make polyester is very odiferous. Because of the quantity of organics in the wastes, it is practical to incinerate the wastes at no net fuel expense and solve the odor problem.
Industrial discharges of sulfide can result in toxic and corrosive conditions. If there is biodegradable material, a source of bacteria and a source of sulfide or sulfate in the industrial wastestreams, hydrogen sulfide gas may be produced under anaerobic conditions in the sewer. Bacteria reduce the inorganic sulfate to sulfide when there is insufficient oxygen in the wastewater (less than 0.1 mg/L), thus producing hydrogen sulfide gas. The sulfide is subsequently oxidized to sulfate by other bacteria under aerobic conditions, producing sulfuric acid which is extremely corrosive to the crown (upper section) of sewer pipes (I.W.T, 1999).
Besides an odor problem, hydrogen sulfide also presents a safety (toxic gas) problem to sewer maintenance personnel and the IWTS operator or, if discharged to the sanitary sewer, the POTW collection system and treatment plant operators. Hydrogen sulfide when dissolved in the wastewater will also produce sulfurous and sulfuric acid, very corrosive materials that attack uncoated metal and concrete surfaces. The anaerobic reduction usually requires a long detention time and an active biological population. Sources of sulfide and sulfate should be identified and recovered or treated prior to discharge. Some suggested solutions to this problem are: require oxygenation and/or chlorination prior to discharge; aerate the wastewater in the collection system; periodically remove the slime layer of anaerobic growth in the system with a slug loading of alkali or chlorine; or periodically clean the sewer with a high-velocity cleaner or a pig (a sewer-cleaning device). Industrial discharges to the POTW containing high concentrations of sulfide are normally restricted. Limitations of 5 mg/L of total sulfide and 0.5 mg/L of dissolved sulfide are used.

1-1-4 pH Problems

The pH of an industrial discharge or the amount of acids and alkalies discharged to an industrial sewer are normally taken into account during design. While older plants in the petroleum, primary metals, and chemical industries have sewers constructed from less corrosion-resistant materials, many of the modern facilities use plastics, fiberglass or other resin material for the industrial wastewater piping and sewer systems. Difficulties can arise when the manufacturing process changes or new chemicals are used that are not compatible with the existing sewer system. For example, fiberglass piping is an acceptable material of construction for sulfuric acid, but if the plating operation adds a process using hydrofluoric acid, the fiberglass may be severely damaged.
The industrial collection system may be designed to handle strong acids or alkalies, but may not be designed to withstand the heat of solution or reaction. For example, when a concentrated solution of sodium hydroxide (such as a spent alkaline cleaner) is discharged to the sewer, there could be a large temperature rise due to the heat of solution. If there is only a small quantity of stagnant wastewater in the sewer or pump station, the heat of solution may exceed 104 degrees Fahrenheit (40 C), the deformation temperature of PVC (I.W.T, 1999). A spill of liquid chlorine can cause a temperature rise sufficient to produce steam resulting in a very toxic gas. Liquid chlorine can also damage plastics directly.
Acids will corrode concrete and cast iron sewers, concrete wet wells and tanks, the internal steel equipment in the primary and secondary clarifiers, trickling filters, aerators, and pumps. Mineral acids such as sulfuric, nitric, hydrochloric, and phosphoric acids are used extensively to clean base metals in the metal finishing industries. The fertilizer, iron and steel, mining, and petroleum industries also use vast quantities of these strong acids. Mineral acids are also used in pretreatment systems for chromium reduction, neutralization of alkalies, and pretreatment of chelated metal plating solutions. Discharge of acid to the sewer from a spill or due to an equipment or control instrumentation failure can cause a pH violation and damage to the collection system. Spill containment provisions are essential in all areas where strong acids or alkalies are being used or stored. Too high a chlorine concentration is also corrosive to the collection system. Many platers will over-chlorinate their cyanide wastewater to ensure they meet the requirements for cyanide concentrations. However, 40 to 50 mg/L excess chlorine can be corrosive to equipment and dangerous to personnel servicing a pump station.
The organic acids such as acetic, maleic, benzoic, oxalic and citric acids are weaker than mineral acids but, nonetheless, can have a pH of 4.0 or less. They too can corrode the sewer or attack the solvent joints of plastic or resin-based sewers. They also represent an organic load to the IWTS. If the pretreatment system does not remove organics, then these acids will represent an organic load to the POTW. Organic acids are typically used in food processing, beverage and consumer product manufacturing, and in the manufacture of chemical intermediates. Strong alkalies can corrode sewers and pumping stations; aluminum is particularly affected by high pH. High pH may also precipitate metals like calcium, potentially causing a solids buildup problem in the sewer. The strong alkalies include sodium hydroxide, lime, and ammonia. These are used in the metal finishing industry to clean and chemically mill base metals. The water treatment industry uses significant quantities of lime to soften water, and pretreatment systems use strong alkalies to neutralize industrial wastes. Because of the potential damage these substances may cause, it is important to periodically review the IWTS spill containment measures and check the failure mode of the chemical addition controls.
The acceptable pH range for the discharge of industrial wastewater to the POTW collection system, as regulated in many industrial waste or sewer-use ordinances, is 6.0 to 9.0. In some ordinances, the pH range may be widened. Remembering that a pH of 7.0 is neutral, the trend is to allow more alkaline or basic material in the discharge rather than materials that are more acidic. The construction materials for sewers, pumping stations, treatment equipment, and biological processes all withstand alkaline discharges better than they withstand the discharge of corrosive acids. However, the discharge of strong alkalies to the POTW sewer may actually be beneficial in removing the anaerobic slime layer from the sewer. When this is allowed, it should be done with the POTW’s permission and knowledge of each discharge so that the POTW influent and secondary treatment can be monitored to prevent a treatment process upset.
The discharge of out-of-pH-range wastewater will result in damage to the sewer. Over a period of time such discharges can eventually corrode the pipe completely, causing exfiltration and contamination of the groundwater or infiltration of the groundwater into the sewer where the groundwater level is above the depth of the sewer. Industrial discharge violations of pH will also increase the maintenance requirements on pumps in the pumping stations. The damage to the pumps could eventually cause their failure, resulting in sewer backups and raw wastewater overflows.

1-1-5 Flammables

The discharge of flammables is potentially the most damaging industrial discharge to the collection system. Gasoline, aviation fuel, and hexane used in soybean extraction have been responsible for explosions in sewers causing losses of millions of dollars for sewers and businesses, the loss of service to hundreds of people, and loss of life. Industries producing, distributing, and using fuels and solvents are regulated and monitored to prevent discharge of these materials. Generally, fuels and solvents are only slightly soluble in water and have a specific gravity less than water. When accidentally discharged to the sewer, they will float and accumulate in slow-moving sewers and in pump station wet wells. Any source of ignition such as an arc from tripping a breaker or a motor, or a spark created while removing a manhole cover with a pick can cause a fire or explosion.
Another concern with flammable wastes is the exposure of industry personnel or the IWTS operator to volatile toxic substances. When solvents are discharged to the sewer and then aerated, they volatilize, thus exposing operators and other personnel to hazardous fumes. This is true of both immiscible solvents and miscible solvents such as acetone, methyl ethyl ketone and isopropyl alcohol. If the concentration of fumes is high enough, an explosive atmosphere may develop. Solvents can also cause the joints of plastic and resin-type industrial piping systems and sewers to fail. In addition, care must be taken when using these types of piping materials because they are also combustible in the case of a fire or explosion. The discharge of flammables to the POTW sewer is dangerous for the same reasons noted above. If the concentration of flammables is high enough, an explosive atmosphere can develop, especially if the secondary treatment process is covered or uses pure oxygen. Any hydrocarbon may cause a flammable hazard in a pure oxygen activated sludge system. However, these systems are usually equipped with sensors and purge systems to prevent flammable and explosive conditions from developing.

1-1-6 Temperature

Heated industrial wastewaters originate from controlling manufacturing process reactions and as a by-product from utilities production of energy. In manufacturing processes, heat is often used to increase the rate of reaction and thus creates a heated product or waste which must be cooled. Water or steam is often used directly or indirectly (by means of heat exchangers) to heat or cool the product or by-product and to transport it to the next processing step. The metal finishing industry uses steam to heat process solutions. Accumulated solids must be removed from boilers to prevent plugging of the boiler tubes and steam lines. The discharge is called boiler blowdown. In cooling systems, single-pass cooling water and cooling tower blowdown can also contribute a heat load to the industrial and POTW sewers. Heated industrial discharges can cause many problems in the IWTS collection and treatment systems including evolution of gases and odors, overheating of pump and rotating equipment bearings, shifts in the population of microorganisms used in biological treatment of industrial wastewater, or even sterilization (killing of all organisms) in the wastewater.
Plastic pipe (PVC) has temperature limitations of around (40 C) and can fail if used for hot water transport (I.W.T, 1999). In the POTW sewer laterals, the O-rings may not be designed to withstand a constant high temperature; if they fail, exfiltration or infiltration of the collection system may occur. The same problems identified in the industrial sewer can also occur in the POTW collection and treatment system. In addition, if the POTW is discharging to a stream or lake with a temperature limit (for example, a trout stream), then a high temperature discharge by an industrial source can cause the POTW to violate its permit limit.

1-2 Effects on the treatment system

Industrial waste discharges damage treatment plant equipment in many of the same ways they damage the collection system. High volume discharges can exceed the pumping capacities; plugging of mechanical equipment such as bar screens or pumps can occur from a high solids discharge; acids and alkalies will corrode metal parts eventually causing failure; and flammables in the treatment plant are an explosive problem that can cause almost instantaneous damage. The added potential problem with industrial discharges is their effect on the treatment processes, including blinding of filters with oil; plugging microfiltration, nanofiltration or reverse osmosis membranes; interfering with recovery processes by contaminating the by-product; and overloading or upsetting the aerobic and anaerobic biological treatment processes.

1-2-1 Hydraulic overload

Unit processes such as neutralization, sedimentation, filtration and biological treatment operate best at a constant flow and constant loading conditions. Large changes in the volume of flow or rapid changes in loading will decrease the efficiency of these processes. Hydraulic surges from an industrial process or utility discharge can cause these rapid variations. To compensate, the treatment plant must make a series of changes in their plant operating conditions, such as changing the sludge removal rate, increasing the blower output, or increasing the chemical addition rate. The alternative is to suffer possible effluent limit violations. Equalization of the flow at the source or installed as a part of the IWTS provides the best means of controlling hydraulic surges and operating the treatment processes at a constant or near-constant flow.

1-2-2 Interference

EPA defines interference as a discharge which, alone or in conjunction with discharges from other sources, inhibits or disrupts the POTW, its treatment processes or operations, its sludge processes, use or disposal, and is a cause of prevents the lawful use or disposal of sludge. This definition of interference applies equally well to discharges by industrial processes to the IWTS. By working closely with the manufacturing and utility operators, the IWTS operator can identify potential interference problems before they cause a discharge violation. Good communication between the operators in the manufacturing facility and the IWTS operator is the most reliable way to identify changes, whether sudden or gradual, in the operation of the plant or quality of the effluent. Discharge of untreated wastes or even large quantities of treated wastes can cause interference with the POTW treatment processes. Table 1 illustrates examples of how industrial discharges may cause potential interference with the POTW’s treatment processes.

Table1 Interference from industrial discharges (I.W.T, 1999)

1-2-3 Influent variability

Measurements of wastewater flow, pH, temperature, and conductivity are used to detect changes in the influent to the IWTS or POTW. As with hydraulic surges, variability in the chemical composition of the influent wastewater can cause upsets in the treatment processes. The larger the difference between the existing influent composition and the contribution from the industrial discharge, the larger the potential for problems. A change of one pH unit represents a ten fold change in the concentration of acid in the influent. Chemical reactions, precipitation, settleability and filterability are greatly changed by the pH of the wastewater. For biological treatment systems, both aerobic and anaerobic treatment are inhibited by rapid changes in environmental conditions. Operation outside of the pH range of 7,0 to 8.5 can be toxic to bacteria; however, if the change is gradual the microorganisms can become acclimated to pH levels slightly beyond this range. Changes in conductivity or ORP (oxidation-reduction potential) normally represent increases or decreases in soluble salts, cyanide or metals. Inhibition or interference can range from overloading the chemical processes with the mass of metals or cyanide requiring treatment to inhibiting the biological reactions. Changes in soluble salt concentrations alter the rate of oxygen transfer through bacterial cell walls and therefore affect the health and performance of the microorganisms.

1-2-4 Slug loadings (also called Shock Loads)

Slug loadings or batch dumps of compatible or noncompatible pollutants from industrial processes, whether accidental or as part of normal production, may cause interference with the treatment processes or pass-through of pollutants. To assess the effect of a slug loading, the mass of the discharge and the resulting concentration at the treatment plant have to be taken in consider. For example, if a concentrated solution containing 45.3 gr of copper is discharged to a biological treatment system, it may result in a concentration of 5 mg/ L for a 5-minute period at the treatment plant. While this is a significant variation from a 0.25 mg/L average influent concentration, the effect on the activated sludge treatment system would be minimal, and the sludge reuse potential would not appreciably suffer from a one-time occurrence. However, if the concentration were to remain at 5.0 mg/L for a one-hour period, the biological treatment system would likely be affected, severely reducing or stopping biological treatment, and the sludge would be contaminated (I.W.T, 1999). The concentration of the slug loading as measured at the treatment plant was the same in both examples, but the second example illustrated a batch dump which was 12 times more mass than the first. It would have caused discharge violations, sludge contamination, and the biological treatment removal efficiencies would suffer until new bacteria could be cultured to return to the previous efficiency. If slug loadings such as in the first example are allowed to continue on a daily basis, organisms in the activated sludge or trickling filter process may become acclimated and the daily discharges probably will not affect the effluent quality.

1-3 Effects on effluent and sludge disposal and reuse

Industrial discharges which, alone or in conjunction with discharges from other sources, pass through the POTW’s facilities to navigable waters and cause a violation of the discharge permit are considered pass-through discharges. Pass-through of compatible and noncompatible pollutants can occur when the POTW treatment system is under stress from hydraulic or compatible waste overloads or shock loadings of toxic pollutants. When the pollutant removal efficiency decreases, the constituents from industrial discharges are found in the effluent. Excluding slug loadings, the constituents most likely to pass through a biological IWTS are small quantities of the toxic organics that are very miscible (Ketones and alcohols, if not stripped, are metabolized by secondary treatment), or immiscible and lipophilic (pesticides or polychlorinated biphenyls) and soluble heavy metals that are not used as micronutrients. The constituents that are likely to pass through a physical-chemical IWTS are small quantities of toxic organics that are miscible solvents or chelated metals. If the toxic constituents in industrial processes are controlled on site, the level of toxics discharged to the sewer is minimal. This optimizes the recycle and reuse options of both the effluent and sludge. Effluent can be further treated for reclaimed water uses; sludge can be applied to land as fertilizer or mixed with a bulking agent and made into compost if it is biological. If the sludge contains a high percentage of metal, it may be reclaimable as an ore by refining or smelting. Industrial processes whose discharges, upset or pass through the treatment system eventually have an effect on the effluent and sludge quality. In essence, the industrial process has contaminated the wastewater. Instead of being a potential resource, the effluent and sludge become a liability.

1-4 Effects on the POTW

Effects of an industrial discharge on the POTW collection, treatment and disposal system parallel those of a manufacturing process waste on the IWTS. There are problems with each component of the system. The Pretreatment Regulations were established to remove toxic pollutants at the source and to protect the POTW’s collection, treatment and disposal systems and the environment. The local Industrial Waste Ordinance specifies the exact operating conditions each POTW must observe to prevent pass-through and interference. The effects of an industrial discharge on the POTW will always depend on the characteristics and flexibility of the system, the level of skill possessed by the POTW inspectors, laboratory analysts, and POTW operators, and the amount and type of industrial flow. Factors such as the size and length of the sewer system also influence how an industrial discharge will affect the POTW collection system. In general, the larger the system, the less effect a single industrial discharge will have on the POTW regardless of whether the industrial discharge is a slug loading or a constant discharge. Dilution and equalization of the industrial discharge occur naturally in the larger collection systems, thereby reducing the effect on the POTW facilities. As the complexity of the POTW treatment system increases from only primary treatment to tertiary treatment, the effect of an industrial discharge also increases. The higher degrees of treatment are more sensitive to upset from industrial discharges. Secondary and tertiary biological processes such as activated sludge, nitrification, denitrification, and anaerobic digestion can be upset by a toxic “overdose” of heavy metals. Tertiary physical-chemical processes such as sand filtration can be rendered useless by a pass-through of oil or a carryover of gelatinous (jelly-like) bacteria from an upset biological process. If the configuration of the treatment system can be easily changed, the effect of an industrial discharge may be lessened. Changing the recycle ratio on a trickling filter or altering the biomass concentration in an activated sludge system could prevent pass-through of noncompatible pollutants or air strip volatile organic compounds. Changing a two-unit process from parallel operation to series operation may help to remove high loadings of compatible pollutants. The disposal of the POTW effluent and sludge are also affected by industrial discharges. The effluent discharge requirements are more stringent for water reuse than for discharge to receiving waters. POTW sludge being used as a component in compost for resale must meet stricter quality requirements than sludge being landfilled. Toxic components of industrial discharges may limit the recycle and reuse options if the POTW is not properly protected from slug loadings or if contaminated concentrations reach a level that may pass through and be discharged in the effluent or sludge. When certain metals reach high enough concentrations in the sludge, then the sludge must be handled as a hazardous waste.

Ref.

1- Abdulrzzak Alturkmani, Dairy Industry Effluents Treatment, Thesis. UTCB University, Bucharest-Romania 2007
2- Brault, Water Treatment Handbook, 1991
3- Califorina State University, Industrial Waste Treatment, V1&V2. USA,1999
4- Eckenfelder, Industrial Water Pollution Control, 1989
5- Kiely, Environmental Engineering, 1996