Water Treatment Plant Residuals

Residuals: They’re not just for chlorine …. References: Small systems residuals  Priority pollutants  Surface Water quality standards and discharges  NPDES program   Filter Backwash recycling Rule   OTHER READING MATERIALS PROVIDED WITH THE COURSE SITE

Residuals: They’re not just for chlorine …. What is a residual?  Water treatment plant residuals can be divided into two categories: The treatment media or chemicals used The contaminants removed from the water  Treatment plant wastes (water and sludge) contain these components in varying amounts

Residuals: They’re not just for chlorine …. Types of treatment which generate residual wastes  Sedimentation:sludge  Filtration:backwash water  Ion exchange:brine, discarded resin  Softening:brine or lime sludge  Membranes:reject water  GAC:Discarded media

Residuals: They’re not just for chlorine …. Treatment chemicals residuals  Depending upon the coagulant used, sedimentation sludge may contain a significant amount of heavy metals.  While only a small volume of coagulant is fed in comparision with the volume of water treated, the coagulant will be concentrated in the sludge after the sedimentation process

Residuals: They’re not just for chlorine …. Sample specification for alum coagulant

Residuals: They’re not just for chlorine …. Sample specification for Ferric Chloride coagulant Impurities shall not exceed the levels set forth in the following table. Impurity Impurity Level mg/L or ppm  Arsenic 80  Cadmium 30  Chromium 80  Lead 80  Mercury 3  Perchlorate 0  Selenium 20  Silver 80

Residuals: They’re not just for chlorine …. Refer to previous topics for discussion of Ion Exchange Residuals  Regeneration brine will contain in a highly concentrated form all of the contaminants removed during the exchange treatment, plus high levels of sodium (salt).  At the end of useful life, ion exchange resins are a solid material to be analyzed for heavy metals, toxics, etc before disposal

Residuals: They’re not just for chlorine …. Refer to previous topics for a discussion of Lime Softening residuals  Lime sludge has a relatively high pH and may contain precipitated contaminants such as iron, manganese, other metals, or radioactive compounds.  If analyzed and found to have a safe level of contaminants, it is possible to utilize lime sludge as a commercial soil conditioner (similar to adding lime to a homeowner lawn).

Residuals: They’re not just for chlorine …. Refer to previous topics for a discussion of Membrane reject water  Membrane reject water is a waste stream of approximately 5 -15% of the total water treated.  The entire quantity of contaminants removed from a large volume of treated water will be present in the reject water at a level of times the original concentration. For example: A membrane plant treats 10,000 gallons of water with a natural nitrate concentration of 1.5 ppm. 500 gallons of reject water is generated, containing all of the nitrate originally present in 10,000 gallons of water. The concentration of nitrate in the reject water is 30 ppm, or three times the Maximum Contaminant Level.

Residuals: They’re not just for chlorine …. Refer to previous topics for a discussion of GAC replacement/regeneration  GAC filter media will adsorb contaminants until its capacity is reached. At that point the media must be replaced so that the treatment plant can continue operation.  After being removed from the filter, the GAC media may be regenerated or discarded. During the high heat of regeneration, contaminants are vaporized off the GAC media and released into the air. Depending upon the type and amount of contaminants, an air pollution emissions permit and/or air scrubbing equipment may be required. If discarded, the media must be analyzed to determine whether or not it must be considered a special or hazardous waste. Depending upon the type and amount of adsorbed contaminants, special waste handling or or hazardous waste permits may be required.

Residuals: They’re not just for chlorine …. Managing Residuals: Concentrate solids to a minimum volume for lower disposal cost  Solids separation techniques include: Sand drying beds Lagoons Sludge Thickeners Vacuum Filters Belt Filters Filter Presses Centrifuges Relies on natural evaporation For solid/liquid separation

Residuals: They’re not just for chlorine …. Types of Mechanical Solids-Separation Equipment EquipmentDescriptionEnd Product Sludge Thickeners Thickens sludge before dewatering After dewatering 5-10% solids Vacuum Filters Pulls water away from the solids with vacuum Slightly wet solids Belt Filters Filter Press Sludge is conditioned with polymer then squeezed to remove water Slightly wet solids CentrifugesRotating action (similar to spin cycle on washing machine) 50-65% solids

Residuals: They’re not just for chlorine …. Disposal of the concentrated solids The most common practice is land-based disposal. Methods include: Beneficial re-use: solids are used as fill material or to stabilize or remediate contaminated soils Land-filling: solids are buried in a lined storage landfill as a non-hazardous, hazardous, or special waste Land application or land farming: solids are applied as nutrients, fertilizers, or soil amendments

Residuals: They’re not just for chlorine …. Making the decision to landfill, re-use, or land-farm Review the following materials (download from the sites below, or supplied with your course materials) Ferric and alum residuals Innovative re-use of water treatment plant sludge 

Residuals: They’re not just for chlorine …. Each waste must be analyzed to determine if it meets the criteria for ‘hazardous’ waste  WTP waste, if it is determined to be hazardous, is most likely to be considered hazardous under the toxicity characteristic. Wastes that contain high levels of readily leachable arsenic, barium, lead, and other toxic compounds (see 40 CFR ) may be considered hazardous.  A common analytical test is the Toxicity Characteristic Leaching Procedure(TCLP) Predicts if hazardous components of a waste are likely to leach out of the waste and become a threat to public health or the environment. If so, land-based disposal options are limited.

Residuals: They’re not just for chlorine …. Paint Filter Liquids Test  Determines if “free” liquids are present in a waste – Wastes containing free liquids banned from disposal in municipal solid waste landfills and hazardous waste landfills – Liquid wastes must be treated or disposed in an alternative manner

Residuals: They’re not just for chlorine ….  Because filter backwash water contains comparatively high volumes of water and low volumes of contaminants, some water systems have chosen to recycle / retreat this water for further use.  Read the Filter Backwash Recycling factsheet (download at the site below, or provided with your course materials)  Filter Backwash residuals: a special combination of liquid and solid wastes

Residuals: They’re not just for chlorine …. Filter Backwash residuals: a special combination of liquid and solid wastes  The majority of systems do not recycle all of their backwash water. A solids separation technique (usually settling basin or lagoon) is used to concentrate the solids (coagulant and settled turbidity particles) for future disposal while the liquid (water) portion of this residual waste is discharged to a sewer or into the environment.

Residuals: They’re not just for chlorine …. Disposing of treatment plant wastewater  After the removal/reduction of solids, the remaining wastewater will be discharged to a wastewater treatment facility or to the environment  Discharges to a treatment facility are subject to pre-treatment requirements established by the receiving facility  Discharges to the environment are subject to the requirements of the National Pollutant Discharge Elimination System (NPDES)

Residuals: They’re not just for chlorine …. Examples of pre-treatment requirements  A local wastewater facility may restrict the maximum allowable rate of discharge so as not to exceed the carrying capacity of sewers  In addition, the concentration of chlorine or other chemicals may be restricted to prevent the microorganism population at the wastewater plant from being reduced or destroyed.  Surcharges may be assessed for chemicals which are difficult to remove/treat such as greases, oils, etc.

Residuals: They’re not just for chlorine …. NPDES Program  States may obtain regulatory primacy for NPDES issues.. In that case, water systems may be regulated under KPDES (Kentucky Pollutant Discharge Elimination System), TPDES (Texas Pollutant Discharge Elimination System) etc.  The principles of the NPDES program remain the same no matter which agency has regulatory primacy.

Residuals: They’re not just for chlorine …. NPDES Program  Review the following information for an overview of the NPDES program: (download from sites below or provided with your class materials) NPDES program  

Residuals: They’re not just for chlorine …. Why are water treatment wastewaters regulated under NPDES? Rivers, lakes and streams are to be maintained in an unpolluted state, available for the support of wildlife, recreation, and human health. Review water quality standards (at the sites below or provided with your class materials) Surface Water quality standards and discharges

Residuals: They’re not just for chlorine …. How could treatment plant wastewater impact stream water quality?  Excessive amounts of chlorine or chloramines can kill fish  Excessive turbidity makes water unattractive for recreation and can impact aquatic life  Concentrated salt brine can kill fish and other organisms  Many metals are toxic to fish: for example zinc (fed in corrosion inhibitors) begins to kill certain forms of aquatic life at a concentration of.7 mg/L and aluminum (used in coagulants) is toxic to some aquatic organisms at.6 mg/L  Metals and other contaminants may settle in stream beds and accumulate to much higher concentrations in the sediment over time.