WASTEWATER PROBLEMS ASSOCIATED WITH SOLVENTS

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1 WASTEWATER PROBLEMS ASSOCIATED WITH SOLVENTS James L. Walsh, Jr., P.E. Senior Research Engineer Georgia Tech Research Institute Atlanta, Georgia Introduction There a number of advantages to elimination of solvents for industrial processes including reduction in hazardous waste generation, improved worker health and safety, and elimination of volatile organic compounds (VOCs) which contribute to air pollution. However, the alternative to the solvent is often an aqueous based material that could present a wastewater disposal problem for a plant. A plant that already discharges wastewater from industrial processes may have no addition problem or may have to make a simple modification to their current treatment system, but a plant that is not currently discharging industrial wastewater may have a significant impact on their operation. This paper presents the major considerations involved in the discharge of industrial wastewater. Wastewater Disposal Methods There are several methods that can be used to dispose of wastewater produced by a plant. Some of these methods require permits as well as monitoring of pollutant levels in the wastewater. A specific facility may be limited to the number of facilities that can be used. Direct Discharge - The direct discharge of wastewater to surface water requires a National Pollutant Discharge Elimination System (NPDES) permit. If a facility does not have an NPDES permit, it is almost impossible to get one. The permit will require some monitoring of pollutant levels and can place limits on the amount of pollutants discharged and the amount of wastewater discharged. A facility with an NPDES permit will most likely have to construct a plant to treat the wastewater before discharge. It should be noted that a stormwater discharge permit is actually an NPDES permit. Discharge to a POTW - Most facilities discharge their wastewater to the sewer which pipes the water to a Publicly Owned Treatment Works (POTW). The POTW then obtains the NPDES permit to discharge wastewater. Wastewater discharges from a plant usually require a permit unless the only wastewater discharged is from the bathrooms. The permit will require some monitoring of pollutant levels and can place limits on the'amount of pollutants discharged and the amount of wastewater discharged. A POTW may also impose surcharges for the discharge of wastewater. A facility with a permit may have to install a pretreatment system to treat the 1

2 I wastewater before discharge. This pretreatment system does not have to treat the wastewater to the same levels as the facility with an NPDES permit. It must remove sufficient pollutants such the POW can then treat the wastewater to NPDES limits. The POTW discharge limits and surcharges will be discussed later. Discharge to a Land Application Svstem - Some facilities spray their wastewater on land where an agricultural crop such as hay or trees are grown. The crop utilizes the wastewater and the carbohydrates and nutrients in the wastewater. Land application systems require a permit. The permit will require some monitoring of pollutant levels and can place limits on the amount of pollutants discharged and the amount of wastewater discharged. The monitoring required often requires the placement of monitoring wells. A facility with a permit may have to install a pretreatment system to treat the wastewater before land application. The major problem with land application is the land required for the system. It can be utilized only by facilities in rural locations. Discharge to a Septic Svstem - The only wastewater that can be safely sent to a septic system is the discharge from bathrooms. Disposal of any other wastewater is not recommended by the state. However, there are no guidelines as to acceptable levels of pollutants that could be put into a septic system. Therefore, discharge of industrial wastewater to a treatment system is not recommended. Evaporation - Evaporation of the wastewater is a safe alternative for plants that do not have an NPDES permit, are not connected to a POTW, and do not have sufficient land for land application. Even facilities that have other options install evaporation systems due to problems meeting discharge limits. Evaporation can utilize large amounts of energy, but the vapors can be condensed and recycled to the process. The sludge or solid residue may require Toxicity Characteristic Leaching Procedure (TCLP) testing to determine if the material is a hazardous waste requiring special disposal. If the material is not hazardous, it may require dewatering and/or drying to meet landfill restrictions on disposal of liquids. An evaporator will also evaporate any VOCs in the wastewater. This might have an adverse impact on an air permit. Trucking Off-Site - Another alternative for wastewater discharge for a facility that is connected to a septic system is to put the wastewater in a tanker truck and transport to another facility that can safely discharge the wastewater. Caution is advised if the wastewater contains any heavy metal or certain chemicals. The wastewater could be classified as hazardous wastewater which requires manifesting the material as hazardous waste, transporting by a permitted hazardous waste transporter, and may require that the facility that receives the hazardous wastewater obtain a RCRA Part B permit to operate as treatment, storage, and disposal facility (TSDF). Discharge of Wastewater to a POTW Disposal of wastewater to a POTW is the most common method used by industry, and, Therefore, the next section will discuss the measurements, limits, surcharges and other factors associated with discharging to a POW. Any industry discharging to a POTW must be 2

3 knowledgeable of these parameters to avoid excessive costs and/or problems. Measurements - The primary measurements required on wastewater are BOD, COD, TSS, TS, Oil & Grease, TKN, TP, and ph. The measurements are reported in milligrams per liter (mg/l) which is equivalents to parts per for water measurements. The procedures for making these measurements are outlined in Standard Methods for Analysis of Waste and Wastewater. BOD - Biochemical Oxygen Demand (BOD) is one of the measurements that is typically made by a POTW. It is essentially a measurement of the organic matter in the wastewater. The standard measurement is BOD, which is the BOD concentration after 5 days of incubation with bacteria. BOD,, is a measurement made after 20 days of incubation and is not commonly used. COD - Chemical Oxygen Demand is not one of the measurement that is typically made by a POTW. It is also a measurement of organic matter but is made using concentrated sulfuric acid. It can be used in place of BOD for analysis of wastewater that contains compounds toxic to organic life. The COD measured will be higher than the BOD, and, if the pollutant level in the wastewater is constant, the ratio of COD to BOD will also be constant. Therefore, a facility can measure COD in a short period of time to get a reasonably good estimate of BOD. TSS - Total Suspended Solids (TSS) is one of the measurement that is typically made by a POTW. It is essentially a measurement of the suspended particles in the wastewater that are not dissolved. - TS - Total Solids (TS) is not one of the measurements that is typically made by a POTW. It is a measurement of the dissolved and suspended solids in the wastewater. Oil and Grease - Oil and Grease (sometimes called fats, oils, and grease (FOG)) determines the amount of these substances in the wastewater. A large amount of oil and grease in wastewater can block sewer pipes by an accumulation of these materials. TKN - Total Kjeldahl Nitrogen (TKN) is the total amount of nitrogen in the wastewater. Nitrogen is a nutrient that must often be festricted due to problems is the surface water to which the POTW discharges. For example, there are TKN limits associated with Lake Lanier. In addition some facilities measure ammonia nitrogen which accounts for the portion of the TKN that has evolved into ammonia. -- TP - Total Phosphorous (TP) is the total amount of phosphorous in the wastewater. Phosphorous is nutrient that must often be restricted due to problems is the surface water to which the POW discharges. 3

4 ~ I pfj - The ph of the wastewater is also measured to prevent an acidic or caustic discharge that could adversely effect the POTW. Other - Depending on the industry, a POTW may measure for metals and other chemicals in the wastewater. Discharge Limits - The typical discharge limits allowed by a POTW are presented in Table 1. These values are only typical and each facility must check with their local POW for exact values for their locality. The table shows the minimum limit. The minimum limit is the concentration of the pollutant that is the worst case expected from a residential discharge. If the concentration of a pollutant in the wastewater is below the minimum surcharges are not imposed. If a facility exceeds the minimum, the facility is surcharged for additional pollutants in the wastewater. The table also shows the maximum limit A facility cannot discharge wastewater with pollutant levels that exceed the maximum, even if they are willing to pay the surcharge. A facility that discharges wastewater with pollutant levels above the maximum could be fined. As indicated in the table, the maximum and minimum limits can be the same. This depends on the requirements of the particular POTW. The table also shows a? for some of the maximum limits. The? indicates that there is a wide variation in maximum limits. The acceptable range of ph for discharge is 6 to 9. Occasionally, a POTW will ask a facility to discharge at a ph higher than 9 to provide buffering capacity to the treatment facility. Table 1. Typical POW Discharge Limits Parameter Minimum (mg/l) BOD 250 TSS I 250 Oil and Grease 1100 TKN I 40 TP I 10 Other None 250-1,OOO -? 250-1,OOO -? loo-? None None 9 Varies Surcharges - Table 2 shows the typical surcharges for discharge of the pollutant if the concentrations are above the minimum limit. These values are only typical and each facility -, must check with their local POTW for exact values for their locality. A surcharge is a fee that the facility must pay to have the POTW treat the pollutant. The alternative for the.facility is to install a pretreatment system to treat the pollutant on-site and reduce the concentration below the 4

5 minimum limit. The cost for the pretreatment system and its maintenance and operation must be balanced against the surcharge for the facility. Note that the surcharges are per pound and the discharge limits are in concentration. The issue of concentration versus poundage limits will be discussed in the next section. Table 2. Typical POTW Surcharges Pollutant Surcharge ($/lb) BOD I $0.15 TSS I $0.10 Oil and Grease I $0.20 TKN $0.70 TP $1.04 Concentration Versus Poundage Limits As shown in Table 1, discharge limits are often specified in permits as concentrations. However, the design of the POW is based on the pounds of the pollutant that can be treated. It is recommended that all facilities obtain a permit based on poundage limits. The laboratory analysis of the measurement of the pollutant will provide the data in concentration which can be converted to pounds if the amount of wastewater discharged is known. If a facility is trying to change their permit from a concentration to a poundage limit, they may need to get a copy of the "Headworks Analysis" for their POTW. This document specifies the design criteria for POW and can be helpful in negotiations with the POTW. Waste reduction is one reason for having a poundage based limit. Many facilities are trying to reduce water consumption in the facility. If the water consumption is reduced and the actual amount of pollutant cannot be reduced, the concentration will increase and the facility may be unnecessarily paying surcharges. The goal of a waste reduction program is to reduce the amount of pollutant as well. Another reason for having a poundage limit is that facilities can often meet poundage limits but not concentration limits. This is usually the case for metals and other chemicals where the concentration limits are small. The Headworks Analysis also provides data on metals and other chemicals. Summary Changing from a solvent to a aqueous based system requires many considerations. One of the considerations is the potential impact on wastewater discharged from the facility. Potential systems should be carefully evaluated to determine this impact. 5

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