B-6176 3-08

On-site wastewater treatment systems

Figure 1: A diagram of separate blackwater and graywater plumbing systems. Graywater Bruce Lesikar1, Rebecca Melton2, David Smith2 and Courtney O'Neill2 1Professor and Extension Agricultural Engineer; 2Extension Assistant, Biological and Agricultural Engineering Department The Texas A&M University System

ith water reuse gaining popularity, people increasingly consider prohibited graywater reuse. In 2003, the th graywater from their residences as a resource to be separated 78 Texas Legislature passed House Bill 2661, providing guidance on residential from the wastewater stream and reused in their landscapes. W graywater system with a capacity less Such reuse of graywater reduces the amount of wastewater entering than 400 gallons per day. This legisla- sewers or onsite wastewater treatment systems, reduces demands to use tion paved the way for broad-scale potable water for other residential uses like irrigation and helps preserve graywater reuse in the state and sought limited water supplies for essential uses like human consumption. This to ensure that water to be reused would be collected, stored and discharged publication discusses using graywater resources simply and legally, at responsibly to protect users’ and their the same time protecting your family’s health, your neighborhood and neighbors’ health and the environment. the environment. To ensure personal and environmental Historically, graywater reuse in such laundry water from wastewater safety, House Bill 2661 also instructs the Texas was limited to reusing laundry drainpipes and diverted its flow to Texas Commission on Environmental water, as homeowners disconnected lawns. However, some jurisdictions Quality (TCEQ) to create regulatory guidance for graywater use. Regulatory Graywater for households equipped with onsite guidance for graywater flows is pre- wastewater treatment systems and for sented in Title 30 of the Texas Admin- separation those plumbed into municipal sewer istrative Code, Chapter 285. In Texas, systems. local authorities generally do not issue To be reused, graywater first Diversion splits blackwater from permits for systems from single family must be separated from blackwater, graywater using two separate pipe residences with daily graywater flow of upstream of any treatment systems. collection systems inside a house, less than 400 gallons. Such separation must be done both running to appropriate fixtures (Fig. 2). Toilet water can be treated with Residential technologies such as non-discharging wastewater toilets (incinerating and composting) or can be directed to a separate onsite sources wastewater treatment system. Once separated, graywater can be diverted Residential wastewater can be di- for reuse, such as for landscape irriga- vided into blackwater and graywater, tion, or it can be directed first to an depending on its source. The Texas onsite wastewater treatment system for Water Code (Code) defines graywater further treatment. Fig. 3 illustrates the as water discharged from four primary components of an onsite  showers wastewater treatment system. Gray- water diverted by a separation system  bathtubs would be introduced upstream of its  handwashing lavatories Figure 1. Wastewater from black- collection and storage components  water and graywater sources, by of the onsite wastewater treatment sinks (not used for disposal of percentage. system. hazardous or toxic materials)  sinks (not used for food prepara- tion or disposal)  clothes-washing machines The Code’s definition excludes water discharged after washing materials soiled with human excreta (e.g., diapers) and wastewater that has contacted toilet waste. Blackwater contains relatively higher concentrations of nitrogen, organic matter and human pathogens than does graywater. Blackwater includes flush water from toilets and urinals and wastewater from food preparation sinks. Fig. 1 illustrates av- erage daily percentages of graywater and blackwater from various sources.

Figure 2. House diagram of separate blackwater and graywater plumbing systems. backing up into the graywater system. Water flowing in the desired direction has enough pressure to lift the flap of the backwater valve and pass through it, but sewage flowing the wrong way forces the flap to stay closed. Two valves are used as a precautionary measure, so that just in case one fails, sewage still cannot back up into the graywater system. Graywater can be collected, treated, stored and reused. The type of Figure 3. Components of an onsite wastewater treatment system. wastewater-treatment system chosen depends on the constituents present in the graywater and on the level of treat- ment desired. In some cases, a settling tank with a gravity-fed pipe to the distribution system may be adequate (Fig. 6). In other cases, graywater can be sent to a secondary tank from which

Figure 4. Diverted graywater plumbing system.

Diverted plumbing systems require wastewater treatment system or to the Figure 6. Settling tank for gravity separate management of blackwater municipal system, but two backwater graywater-distribution system. and graywater sources. Because gray- valves must be installed. A backwater water systems may be used seasonally, valve (Fig. 5) allows water to flow may need periodic maintenance, or one way (to the onsite wastewater it will be pumped to a pressurized may be abandoned in the future, a di- treatment system or to a municipal subsurface reuse system (Fig. 7). In a version valve should be placed in the sewer) but prevents effluent from pressurized system, discharge is regu- graywater collection line at the point lated to control graywater application. where it leaves the residence (Fig. 4). Such control can be important when This diversion valve allows graywater graywater is reused for irrigation. flow to be directed to the graywater With either design, an overflow system or to the onsite wastewa- pipe must be installed to divert excess ter treatment system (OWTS). If a water to the onsite wastewater treat- residence is connected to a municipal ment system or to the municipal sewer wastewater treatment system, the system. When an onsite wastewater diversion valve will direct graywater treatment system is used, however, it either to the graywater system or to may be easier to treat all wastewater the municipal collection system. Figure 5. Backwater valve for from a residence for reuse rather than Overflow from the graywater plumb-ing into graywater system treat graywater separately. A decision system must be diverted to the onsite overflow line. to divert, collect or treat graywater Graywater collection and storage In a limited number of situations (system in existence prior to January 6, 2005), graywater from residential clothes-washing machines may be dis- charged onto the ground using a grav- ity flow system. Graywater from other sources should be diverted through Figure 7. Settling tank and pump tank for pressurized graywater distribution. settling tanks and pump tanks for later treatment and distribution. However, graywater contains organic matter, or to separate wastewater streams at position (Table 1). Constituents likely and if it is stored, it will quickly turn all should be based on an individual to be found in a particular graywater septic, generate offensive odors and household’s circumstances and on the source should be compared to the promote growth of pathogenic micro- purposes for which graywater will be intended reuse application for water organisms. Thus, it is critical to size reused. from that source. Such evaluation also the graywater settling tank and pump helps to identify treatment necessary tank appropriately, so that they do not Graywater prior to graywater reuse. hold graywater for extended periods of time. Generally, to keep graywater system design Graywater yields fresh,it should be stored for less than one day, a critical consideration if The amount of graywater a house- considerations it is to be dispersed onto the ground hold generates depends on number of surface. Graywater sources occupants, their ages, their lifestyle characteristics and their water-use Texas graywater rules also require A homeowner first must decide patterns and on the potential graywa- that graywater be collected in an ap- which household graywater sources to ter sources to be fed into the system proved tank that collect for reuse. Collecting graywater (Table 2). Total amount of graywater  is labeled clearly as “non-potable from all sources increases the risk of produced varies from site to site and water”; additional solids and other pollutants must be estimated as part of system- being added to the graywater. Each design processes.  restricts access, especially to source contributes different contami- children; nants due to its particular water com-  eliminates habitat for mosquitoes and other vectors;

Table 1. Constituents of wastewater from different sources (Wright, 1996).

Water sources Bacteria Bleach Food particles Grease and oil Hair High pH Hot water Nitrogen Odor matter Organic Phosphorus Salinity Soap Sodium Suspended solids Turbidity Shower and bathtub • • • • • • • • Sinks (other than kitchen) • • • • • • • • Laundry • • • • • • • • • • • • Table 2. Estimated residential water use based on house size.

Daily water use Daily water use (gallons) (gallons) (50%) Daily (50%) Daily No. Size of house Without water- graywater With water- graywater bedrooms (square feet) saving devices production (gallons) saving devices production (gallons) 1 or 2 Less than 1,500 225 113 180 90 3 Less than 2,500 300 150 240 120 4 Less than 3,500 375 188 300 150 5 Less than 4,500 450 225 360 180 6 Less than 5,500 525 263 420 210

 can be cleaned; and Graywater bidden. Other good-sense guidelines  help protect human and environmental meets structural requirements of distribution health: the 2004 American Water Works Approved reuse applications.  Edible root crops probably should Association (AWWA) standards. Texas graywater regulations allow not be irrigated with graywater. graywater to be reused in the follow- Settling tank and pump tank capaci-  ties must be adequate for estimated ing ways: Use graywater for well-estab- lished plants rather than for graywater production, expected stor-  around the foundation of a new seedlings. age time and reuse application. The house to minimize soil movement graywater settling tank should hold or cracking;  Graywater usually is slightly about one day’s production volume to alkaline, so avoid using it to water  for gardening; limit graywater detention in the tank plants that thrive in acidic soils. to less than a day and to collect gross  for composting; or  solids on the tank bottom. Inlet and  To prevent salt accumulation, outlet pipes can be close together to for landscaping at a single family distribute graywater over a large allow fairly direct flow between them. residence. surface area and rotate distribu- tion from one area to another. An effluent screen should be placed in To determine the most appropriate the outlet piping to collect debris that use for graywater, consider the con-  Select reuse applications appro- might otherwise exit the settling tank stituents expected to be in the water, priate for the amount of water to with discharged graywater. the constituents to be removed during be generated in the system. treatment processes, and the amount Pump tank capacity is determined Surface discharge exemption. of graywater available for distribu- based on the pump’s minimum operat- Texas regulations include special rules tion. For example, graywater used to ing level, dose volume and alarm for laundry graywater systems in use maintain moisture around foundations volume. These three factors usually before January 6, 2005. According would require less treatment than equate to a pump-tank minimum to 30 TAC Chapter 285 Subchapter would graywater used to irrigate salt- volume equal to two days of flow, H. Section 285.81, a homeowner that sensitive trees or specimen plants. assuming graywater will be dosed to has been discharging laundry wa- a distribution system daily. However, Texas graywater rules dictate ter directly onto the ground surface pump tanks may be larger, based on acceptable methods of graywater dis- (without a settling tank) since before your landscape irrigation schedules. tribution. Generally, graywater should January 6, 2005, may continue to do Some individuals may choose to ir- be applied subsurface. Distribution of so if the area onto which the laundry rigate only a couple of times a week, graywater using a spray system is for- graywater is applied requiring larger tank capacity.  does not create a public heath Subsurface distribution. Although minimize potential health risks and nuisance, surface discharge (except for spray- odors. An example of subsurface  ing) is allowed for treated graywater, distribution includes graywater dosed supports plant growth or is sodded graywater reuse should be distrib- to a gravel bed or trench underlying a with vegetative cover, uted strictly below the soil surface to flowerbed (Fig. 9); water not taken up  does not have wet soil,  does not have surface ponding, and  has limited access and use by resi- dents and pets. This rule also states that a discharge line must have a lint trap and that use of detergents with significant amounts of phosphorus, sodium or boron should be avoided. If at any time the system is altered, creates a nuisance or dis- charges water from sources other than a clothes-washing machine, a previously exempt laundry graywater system will no longer be authorized to discharge to the surface. Such laundry water then must be directed to a graywater system meeting current regulations or into an onsite wastewater treatment system. Graywater systems installed after Figure 8. Laundry graywater system with small settling tank and drag hose for January 6, 2005, must follow the irrigation. criteria of Section 285.81 that allow for discharge above the surface so long as provisions of this section are met. Under this rule, washing-machine discharge first must pass through a graywater settling tank, and the surface drag hose or piping must be purple to denote a nonpotable water conduit (Fig. 8). This color requirement can be met by using pipe painted purple, purple pipe or pipe taped with purple metallic tape. Homeowners should discharge graywater to the surface only from systems for which laundry graywater is the exclusive source. If a homeowner desires to discharge graywater for sur- face reuse, other than from a laundry o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o system, he or she can install a gray- water or secondary treatment system complying with all rules for onsite wastewater treatment systems as listed in Chapter 285 regulations. Figure 9. Graywater system with gravity distribution through a gravel media trench. by plants then percolates through the cially during peak water-use months. Regulations regarding graywater soil profile. The soil provides water Graywater reuse alone may not be suf- systems do not provide specific guid- treatment through physical (filtration), ficient to meet plant peak-water needs ance on distribution-system sizes, chemical (adsorption and transforma- for high-water-use lawns, but it may so designers can size a system based tion) and biological (degradation and provide enough water for small flower either on irrigation requirements or on predation) processes to kill off harmful beds and planter boxes. soil absorption. pathogens. An in-line filter should be installed If system size is based on irrigation Graywater systems equipped to remove any particulate matter that requirements, distribution areas must with pump tanks can disperse water might clog discharge pipes or irriga- be designed to meet summer-month through a pressurized subsurface drip tion emitters. The filter type needed water requirements for landscape system to irrigate trees, flowerbeds depends upon amount of graywater to plants. During winter (or in lower- and planter boxes (Fig. 10). If gray- be filtered and types of contaminants water-use months), graywater must be water will be used for irrigation, it is expected. No matter what filter type is diverted to an onsite wastewater treat- important to know how much water used, it should be cleaned periodically ment system or a municipal sewer to will be available for reuse, so that the in order to prevent it from clogging prevent oversaturating the soil, result- irrigation system can be sized ac- or reducing flow to irrigation fields. ing in less treatment of the graywater. cordingly. Reuse system design also Automatic backwashing filters are Distribution-system sizing based on should consider typical supplemental available and can limit clogging risks. soil-absorption requirements may not water requirements of plants, espe-

Figure 10. Graywater system using pressurized distribution in a subsurface drip system. meet plant water requirements during Required Distribution Area (ft2) = graywater could be exposed to peak-water-use months. However, 300 gal/day ÷ 0.25 gal/ft2-day disease-causing organisms. such sizing can follow the guidelines Required Distribution Area = 1,200 ft2  Water used to launder clothing for the soil-absorption component soiled by pesticides or other toxic of an onsite wastewater treatment Advanced systems are available substances should not be dis- system. These sizing guidelines are solely for treating graywater. However, charged into a graywater system. based on type of soil accepting the instead of spending money on such a wastewater and present the long-term treatment system, it may be more cost  As with any water treatment acceptance rate of the soil based on its effective to forgo a graywater system system, regular operational and classification into four texture-types all together and upgrade your onsite maintenance checks must be per- with specific long-term acceptance wastewater treatment system to a level formed. rate for each classification (Table 3). that can produce effluent meeting wa-  If anyone becomes ill after expo- ter-quality standards for surface or drip Distribution-trench area or drip-dis- sure to graywater disposal areas, reuse (30 TAC Chapter 285). tribution area can be estimated using discontinue using your graywater these sizing factors. Divide graywater- system until you have determined system-designed-flow by the appro- Safety concerns the source of the illness. priate soil sizing factor to determine To protect yourself, your family and distribution-system required square your pets, you must understand that Municipal footage. (Soil must be present around what is washed down sinks and show- the trench or drip distribution system ers into a graywater reuse system will wastewater to accept and treat the graywater, re- eventually end up in your yard. Fol- ducing risks of contaminants reaching lowing are a few safety tips to consider treatment our water resources.) when using such systems: systems Required Distribution Area (ft2) =  If a resident of your home comes The preceding information about Design Flow (gal/day) ÷ Acceptance down with a contagious sickness, 2 using advanced graywater treatment Rate (gal/ft -day) it may be wise to divert graywa- has been directed toward households ter from the house to an onsite For example, to distribute a gray- not connected to municipal sewer wastewater treatment system or to water flow of 300 gallons per day on a systems. Homes connected to sewer a municipal sewer until that indi- sandy loam soil would require a distri- systems can install additional subsur- vidual has recuperated. Otherwise, bution area of 1,200 square feet. face graywater-reuse systems and/or anyone coming into contact with laundry- graywater systems. Texas regulations for such systems are found Table 3. Long-term acceptance rates for different soil types. in Title 30 of the Texas Administrative Code Chapter 210, Subchapter F and Long-term are nearly identical to those described acceptance Soil classification rate (gal/ft2-day) in Chapter 285. The only differ- ences between these code sections are Class Ib (sand, loamy sand) 0.38 specifications in Chapter 210 that (1) Class II (sandy loam, loam) 0.25 graywater can be diverted to an orga- nized water collection system, rather Class III (sandy clay loam, sandy clay, clay loam, silty clay 0.20 than to an onsite wastewater treatment loam, silt loam, silt) system as mentioned in Chapter 285 Class IV (silty clay, clay) 0.10 and (2) graywater-system construc- tion, including storage and disposal components, must comply entirely with Chapter 210. Minimizing  If you use a laundry-graywater or inspection if it conforms to the fol- surface-discharging system, pe- lowing guidelines: blackwater riodically move the drag hose to  Less than 400 gallons of graywa- prevent graywater from ponding ter are used each day for domestic generation in the landscape. purposes. Using composting or incinerating  If you use a pressurized system,  The graywater must come from a toilets in a home dramatically decreas- periodically replace the pump as it single-family dwelling. es the blackwater-waste stream. Sinks fails.  used for food preparation or disposal  The system must be designed so are considered blackwater sources. The particular technology you use that 100 percent of the graywater Therefore, a wastewater treatment to distribute graywater will have can be diverted to the owner’s system still is needed for the kitchen- specific operation and mainte- onsite wastewater treatment sink flow. This type of reuse-treatment nance requirements. More infor- system through two backwater system then would be treated as an mation on servicing a particular valves or backwater preventers; onsite wastewater treatment system, technology is available from these connections must be located falling under the rules in Chapter 285. Texas Cooperative Extension’s in the line between the house onsite wastewater treatment fact stub-out for the onsite wastewater Maintaining a sheet series. It can be accessed treatment system and the onsite from the Web at http://ossf.tamu. wastewater treatment system graywater edu. pretreatment tank. system  The graywater must be stored in Summary of tanks: To keep them working properly, all Texas graywater • that are labeled clearly as treatment and reuse systems require non-potable; some level of attention to their opera- regulations tion and maintenance. The system’s • that have restricted access; designer should provide specific Texas Administrative • that eliminate habitat for guidelines for maintaining your sys- vectors; tem. Some general guidelines follow: Code Title 30, Chapter • that can be cleaned; and  Clean the effluent screen at least 285 Subchapter H. annually. Remove the screen and Section 285.80. • that meet the structural spray residuals off into a large standards of the 2004 This section lays out general re- bucket. Once the effluent screen American Water Works quirements for graywater. It gives the has been replaced into the settling Association (AWWA) definition of graywater used above and tank outlet, slowly pour washwa- standards. (Look for a stamp notes that all construction of gray- ter back into the settling tank. indicating the tank meets water systems must comply with the AWWA standards.)  Remove accumulated solids guidelines of Chapter 285, as well as from the settling tank. Contact a with any more stringent requirements  The graywater system must use wastewater pumper to pump out set by local permitting entities. piping that identifies the water as the solids. Remove solids when non-potable; such piping may be they occupy about 25 percent of Texas Administrative purple pipe, pipe painted purple the tank’s depth or about every 3 or pipe taped with purple metallic to 5 years. Code Title 30, Chapter tape.  The graywater system may not 285 Subchapter H.  The graywater should not be ap- be needed during the entire year. Section 285.81 plied at a rate that may result in During seasons it is not used, set ponding, pooling or runoff across This section defines criteria for the diversion valve to direct flow property lines or onto paved sur- disposal of graywater. An onsite gray- to the onsite wastewater treatment faces. water system is not subject to permit system or to the municipal sewer.  The graywater may not create a for gardening, composting or land- Texas Administrative Code Title 30 nuisance or damage the quality of scaping at a private residence. The Chapter 210, Texas Commission on surface water or groundwater. installer of the graywater system must Environmental Quality  instruct the owner on basic operating The graywater cannot be disposed and maintenance procedures, includ- Wright, M. 1996. Safe use of house- of using spray distribution. ing the system’s effects on an onsite hold graywater. Guide M-106. Las Cruces, NM: Cooperative Exten- If any of these requirements for wastewater treatment system. All Texas Commission on Environmental sion Service, New Mexico State a graywater system are not met, the University. system must meet the requirements Quality (TCEQ) rules and regula- for an onsite wastewater treatment tions can be accessed from the Web system, as described in the rest of at http://www.tceq.state.tx.us/ rules/ Acknowledgment Chapter 285. Installing a graywater indxpdf.html. This material is based upon work system does not allow reduction in the supported by the Cooperative State size of the onsite wastewater treat- References Research, Education, and Extension ment system. Graywater may be used Texas Administrative Code Title 30 Service, U.S. Department of Agri- around the foundation of a new house Chapter 285, Texas Commission on culture, under Agreement No. 2005- to minimize movement or cracking or Environmental Quality 45049-03209.

The On-Site Wastewater Treatment Systems series of publications is a result of collaborative efforts of various agencies, organizations and funding sources. We would like to acknowledge the following collaborators: Texas State Soil and Water Conservation Board USEPA 319(h) Program Texas On-Site Wastewater Treatment Research Council Texas AgriLife Extension Service Texas Commission on Environmental Quality Texas AgriLife Research USDA Water Quality Demonstration Projects Texas On-Site Wastewater Association Consortium of Institutes for Decentralized Wastewater Treatment USDA Natural Resources Conservation Service