Using Graywater and Stormwater to Enhance Local Water Supplies An Assessment of Risks, Costs, and Benefits (2016) / Chapter Skim
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6 State of Design Practice for Stormwater and Graywater
6 State of Design Practice for Stormwater and Graywater
Pages 94-120
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From page 94... ...
Chapter 1 outlines a range of objectives that may be Typical graywater systems are designed to supply water associated with on-site graywater or stormwater projects, for irrigation and/or toilet flushing. A key factor is matching such as providing a cost-effective alternative water supply, the graywater supply with demand so that the resource is diversifying the water portfolio, reducing runoff volume and managed efficiently.
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From page 95... ...
. Determine Project and Design Objectives Determine Quantity, Quality, and Timing of Runoff and/or Graywater Available Evaluate Demand for Available Captured Water Considering Available Applications Evaluate Feasibility of Beneficial Use Based on Generation, Demand, and Scale Evaluate System Design Alternatives; Select System Design and Treatment Train Select Appropriate Unit Processes FIGURE 6-1 Typical steps to evaluate feasibility of and to design a graywater and stormwater beneficial use system.
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From page 96... ...
. Neighborhood-scale graywater reuse where freezing temperatures are observed in winter months, removes the burden of maintenance from the homeowner graywater is diverted to a wastewater collection system for and enables centralized quality assurance inspections to en- those months to prevent breaks in the distribution plumbing.
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From page 97... ...
State of Design Practice for Stormwater and Graywater 97 FIGURE 6-2 Plumbing for separate collection of graywater. SOURCE: Bergdolt et al.
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From page 98... ...
Maintenance was not an issue for users of laundry-to-landscape systems, but it was for users of the system to use graywater to flush toilets. states,1 specifies a maximum graywater storage time of 24 Graywater Treatment Design Considerations hours for irrigation and 48 hours for toilet flushing.
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From page 99... ...
at the household scale tion. Organic carbon or solids removal for single residence are less clear, because pathogen data for graywater are ex- irrigation is required in five states that currently allow graytremely limited.
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From page 100... ...
. TABLE 6-4 State Water Quality Standards for Graywater Reuse for Toilet Flushing Total Coliform Fecal Coliform BOD5 (mg/L)
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From page 101... ...
tion, with the potential concern associated with the formation of disinfection by-products. When treated graywater is Spray Irrigation used for toilet flushing, the ultimate fate of those disinfection by-products is a wastewater treatment system, where they If graywater is to be used for spray irrigation, then it may or may not be removed from the water depending on must meet state water quality requirements for unrestricted treatment practices.
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From page 102... ...
TABLE 6-2-1 Summary of NSF 350 Water Quality Requirements for Toilet Flushing Class Ra Class Cb Measure Test average Single sample maximum Test average Single sample maximum CBOD5 (mg/L)
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From page 103... ...
and the potential for human contact with graywater is high Stormwater regulations may dictate hydrologic, hydraulic, (e.g., toilet flushing or spray irrigation) , lack of proper main- water quality, or design objectives.
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From page 104... ...
performance achieved, in terms of reducing stormwater run off, by larger storage tanks for a research site in Kansas City Stormwater Capture and Tank Storage for roofs about 1,000 ft2 (92 m2) in area (Pitt et al., 2014)
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From page 105... ...
State of Design Practice for Stormwater and Graywater 105 FIGURE 6-6 Surface and subsurface cisterns as part of rooftop stormwater capture systems. SOURCE: City of Bellingham (2012)
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From page 106... ...
This is particularly true in areas with abundant from entering and breeding in stormwater storage tanks. precipitation, such as the central or eastern United States.
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From page 107... ...
. FIGURE 6-8 Recommend ed treatment processes for captured stormwater for var ious end uses and regulatory requirements.
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From page 108... ...
In absence of these tions that minimize human exposures, such as drip irrigation data, a typical conservative approach bases the treatment deor restricted access to a spray-irrigated site, no treatment is sign on known or estimated concentrations of fecal indicator needed other than removal of suspended solids to prevent bacteria; but these may be poor indicators of the presence or clogging (see Figures 6-8a and 6-8b; see also Chapter 5)
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From page 109... ...
storage tanks are often used in neighborhood-scale stormwa- At the neighborhood or large-building scale, real-time, ter collection systems and come in a range of designs, from logic-controlled release of captured stormwater can be used traditional tanks to large subsurface storage units (see Box to optimize water conservation and meet water quality objec tives. These operations are usually designed as part of com bined sewer overflow and stormwater management activities and discharge captured stormwater based on predictions of the amount of runoff for a coming rain.
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From page 110... ...
subsequently withdrawn to irrigate the community gardens Groundwater recharge projects using stormwater can and other on-site landscaping. Pre-treatment prior to storage be designed along an array of scales from small, householdin stormwater capture projects also frequently includes the scale rain gardens to neighborhood-scale biofilters to regionuse of hydrodynamic stormwater treatment systems for gross al-scale aquifer recharge projects.
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From page 111... ...
Household-scale Groundwater Recharge: Rain Gardens Rain gardens are popular on-site controls that have low costs and can significantly reduce the discharges of roof runCapture, Storage, and Infiltration. At the household scale, off from homes.
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From page 112... ...
Biofilters rely upon soil treatment, sometimes area, especially when constructed in conjunction with other amended with engineered media, to provide treatment of the stormwater control elements (such as grass filtering swales percolating stormwater to decrease the groundwater contamiand storage tanks) forming an effective treatment train.
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From page 113... ...
to be effectively re- 5 See http://dnr.wi.gov/topic/stormwater/standards/postconst_stan dards.html. FIGURE 6-13 Percentage reduction in annual roof runoff with rain gardens for Kansas City.
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From page 114... ...
114 Using Graywater and Stormwater to Enhance Local Water Supplies: An Assessment of Risks, Costs, and Benefits FIGURE 6-14 Biofilter/swale under construction with underground wa ter storage vaults for irrigation use. SOURCE: Photo by Dan Bourdeau, Geosyntec, Inc.
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From page 115... ...
In sists of allowing basins to sufficiently dry between wetting current practice, no standard design criteria exist for storm- events; to that end, when possible, operators use a battery of water treatment for large groundwater infiltration projects. infiltration basins to regulate the specific placement of water At the spreading basins managed by the County of Los at the facility to leave some basins empty long enough to Angeles, no additional treatment is provided beyond soil properly dry (Batman, Los Angeles County Department of aquifer treatment, but during a storm event operators moni- Public Works, personal communication, 2014)
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From page 116... ...
Based on the appropriate 2. Graywater is treated for toilet flushing, and storm- treatment system and desired water quality for the end use, water is used for irrigation and/or supplementing unit processes can be selected.
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From page 117... ...
However, there is a lack of Graywater reuse for toilet flushing requires plumbclarity on the appropriateness of surface drip irrigation with ing components and treatment systems that are most apno landscape cover, because the risk of this practice remains propriate in multi-residential buildings or neighborhoods. poorly defined at the household scale.
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From page 118... ...
Many gray- design standards for dissolved organic carbon and turbidity water quality standards are based on state standards for unre- that prevent aesthetic and maintenance issues while allowing stricted urban use of treated wastewater, discharge of treated proper function of disinfection systems when using graywater wastewater to water bodies, or other standards for very dif- for toilet flushing. ferent applications than use of graywater for toilet flushing.
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From page 119... ...
e Coagulation Turbidity: 82-91%f None DOC Biological aerated filters Effluent BOD < 20 mg/Lg No specific graywater considerations g Sequencing batch reactors Effluent BOD < 20 mg/L No specific graywater considerations g Membrane bioreactors Effluent BOD < 4 mg/L No specific graywater considerations g Constructed wetland Effluent BOD 0.7-80 mg/L No specific graywater considerations Soil Aquifer treatment Not Applicable Not Applicable b Sand filtration Effluent BOD 62 mg/L Several successful applications, good fit technology COD: 37-61%b,c,d Membrane filtration Effluent BOD 86 mg/L (UF) ,h 1.5 mg/L Potential for fouling is high, but can be reduced with (RO)
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From page 120... ...
For many locations, the design and roof runoff with low to moderate exposures, additional patho- performance standards for stormwater infiltration have been gen data and risk analyses are needed to establish a consistent developed to address surface water regulatory drivers rather state of practice for on-site stormwater use. Collection, stor- than the protection of groundwater quality from stormwater age, and treatment technologies are mature and can be readily infiltration.
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