CCAT greywater 2017: Difference between revisions

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Background

The first CCAT installation of a constructed wetland for the purpose of greywater treatment was in 2007, and was meant to serve as demonstrative, self-sufficient irrigation system. However, after CCAT relocation in 2007, the project was handed down to the ENGR 305 class. Their first design was implemented in 2008, followed by a second attempt in 2009 which built on the existing system installed. However throughout its life and structural fluctuation, the design purpose of CCAT’s greywater marsh has remained consistent and intended to be multi-purpose: integration of wetland technology, sustainable greywater management strategy and educational opportunity. Both projects (2008 and 2009) encountered problems that dealt with an array of complexities, but most notably are the difficulties that arose in designing efficient and adapted components of the system such as a primary treatment system for kitchen wastewater (as marsh technology is considered secondary treatment), a structurally sound surge tank, and efficient baffles that divert the water in a “maze-like” fashion. The key to an efficient constructed wetland is adaption of the system to complement the local environment meant to house it. Essentially, a constructed marsh is meant to replicate aerobic processes via microorganisms that are sustained by the plants planted in the wetland. Both artificial and organic wetlands are used as a means of secondary water treatment, presenting a perfect design opportunity to treat greywater for the purpose of irrigation.

Problem statement

The objective of this project is to redesign and rebuild the greywater marsh system for CCAT. Our first goal is to update the surge tank, which is anticipated to be one of our most difficult tasks as the surge tank is currently in a deep hole with little access and is covered by two heavy metal grates. The surge tank is necessary to temporarily store the water during high water use times so the marsh has time to process all of the greywater properly. In addition the filter in the current system is located inside of the surge tank, and was originally made of burlap then failed and a mesh and plastic filter was installed. We are envisioning the installation of a woodchip biomass filter above the surge tank to filter out grease and food particles. Other updates will include leveling the ground at the basin of the marsh and updating the pond liner, possibly using a new lining material. As well as updating the baffles that assist in increase greywater-to-oxygen contact and slowing down the water flow to elongate the process of phytoremediation. Introducing more native marsh species that can also assist in the process will be worked on as well. In addition, we will look into the testing tank as the elevation of outlet pipe from existing marsh (approx. 4' below soil surface), has been an issue over the years. To fix this issue we hopefully plan on burying the outlet pipe so that the flower beds can be gravity fed.

Literature Review

This is a review of the available literature pertinent Greywater Marshes

Defining Greywater

The EPA defines greywater as “reusable wastewater from residential, commercial and industrial bathroom sinks, bath tub shower drains, and clothes washing equipment drains.” Discharge from kitchen sinks is usually not considered greywater because of higher concentrations of organic material present in the form of cooking oils and solids. Greywater is categorically different from blackwater, in that it does not contain any fecal matter. Blackwater is defined as the the discharge from toilet outlets, and kitchen sinks in some literature. The high concentration of pollutants in blackwater create a site for bacterial growth that is potentially harmful to humans upon exposure.

Potential Risks

When thinking about installing a greywater system, a lot of people worry about the risks that accompany the reuse of household water. Such risks for the human body include the presence of pathogens from the digestive system, and food handling pathogens. Such pathogens can cause disease through direct contact or the consumption of greywater plants and/or through mosquitos. Risks that accompany the reuse of water for the environment are the possibility of phosphorus in greywater being a risk to your local waterways producing eutrophication. It is clear that sustainable greywater reuse is possible without risking an overdose of phosphorus in the environment, but only if the system is correctly set up. Additionally, a lot of people worry about the possible contamination of soils and aquifers from certain chemicals, oil,s and minerals that may change the soils characteristics. One worry is the salinization of soil, which reduces plant productivity. This is because of the use of laundry detergents and many other household cleaning materials that contain high amounts of salts. In order to reduce this problem, you will need to change some of your household materials.^[1] Other environmental hazards are xenobiotic organic compounds that are found in aquatic animals present in the resulting water. These compounds end up in the water from drugs and antibiotics that somehow end up in the greywater. This is a situation where you will need to keep close regulation of the things you put down your sink. Last but not least are surfactants, compounds that lower the surface tension between two liquids or between a liquid and a solid. Surfactants are used as detergents, emulsifiers, dispersants, foaming agents, etc… Although (as mentioned previously) you can use detergents that are not harmful for the environment, even the biodegradable compounds can reduce the ability of the soil to absorb water.^[2]

Although, if setup properly, these risk s can be minimized to completely reduced through rhizomes in order to remove the excess nutrients (phosphorous) and possible pathogens, and Biofilter to remove many sediments, salts, surfactants and minerals that can harm the soil. All of these mitigations are listed below in the <Types of Greywater Management Systems> section. Although it is important to remember: “To date, no epidemiological survey supports claims that greywater usage at a single household scale is associated with higher morbidity.” ^[3]

Chemical Composition

The chemical composition of greywater is reflective of the households lifestyle. Any compounds used in soaps, detergents, hygiene products, etc. have the potential to be exposed to the installed greywater system and therefore have the potential to make up the composition of the subsequent greywater. Because of this the quality of greywater from any establishment is dependent on the inhabitants living standard, cultural norms, chemical usage and general lifestyle. ^[4]

The highest concentrated nutrients found in greywater are nitrogen and phosphorous. The majority of the nitrogen is deposited via kitchen sink discharge while the majority of phosphorous is originally contained in detergents and soaps, deposited via laundry units.

Legalities

Generally in the United States, municipalities are responsible of collection and regulation of both greywater and blackwater. Although it is becoming more common to see greywater systems throughout California and many other parts of the United States. Below is a [Photo] depicting the cans and cannots of current state legislations. In CA and AZ, the current greywater law is a tiered approach that allows you classify your utilization according to the size of your system. The first tier allows homeowners to divert their laundry water to water gardens without a permit. The second tier does require a permit, and provides you with regulations for a more complex system. ^[5]

There are many different standards for greywater reuse around the world, and the variation between these policies is great. In order to help people in other areas of the world from risk where there isn’t much regulation Maimon et. al. has provided a way to to your own grey water risk assessment (quantitative microbial risk assessment or QMRA) of public health through Hazard identification, Exposure assessment, Dose-response characterization, and risk characterization. ^[6] It is also critical to outline the local “governance” of your location in order to make sure that your system is up to code.

Client Criteria

Education

As [CCAT] ^[7] is designed as a laboratory for sustainability, the greywater marsh has gone through many different phases in the past. One of the problems with the past systems is that people were unable to get an educational value out of the marsh system. [CCAT] is interested in the new greywater project to provide a way to educate people on how helpful a greywater system can be for a person's home.^[8] Some ideas for implementation of this educational value are a truth window. Truth windows are said to be an important aspect of appropriate technology because they give viewers the opportunity to understand that the makeup of their project actually isn't that complicated and can significantly reduce domestic water consumption. In addition, we are interested in using this truth window to help tackle social norms that concern the impact of greywater on human and environmental health. It has been proven that if done correctly, greywater is not a threat to human or environmental health.^[9] There will be a truth window installed in the irrigation system in order to show that the water produced by the greywater system is crystal clear. We will be providing an information sign near the greywater system outlining greywater regulations from around the world, as well as answering questions about why greywater isn’t bad for your health.

Workability

CCAT’s main issue with the greywater system is simply that it has been put together in a fashion that does not properly filter the water. The gravity fed system is not producing enough velocity. In order to meet their needs we will be installing a new irrigation system for the garden bins at CCAT that is fed by a [Siphon] described in the below design mechanisms.

Types of Greywater Management Systems

Within in the context of prolonged drought conditions and controversial water allocation projects in California, alternative on-site greywater reuse systems have gained much momentum locally. ^[10] On a larger scale, these systems have been popularized in low and middle income countries where management services are inadequate or non-existent. Within these nations, if drainage infrastructure exists untreated greywater is discharged into storm drains and diverted into established aquatic systems. This compromises the health of these ecosystems, altering characteristics such as turbidity, nutrients and microbial content, chemical composition, etc. and can to imbalances such as eutrophication.^[11] Where infrastructure is not present, untreated greywater is simply diverted into streets or open ground, presenting multiple risks to public health such as water-born diseases.

Water scarcity, lack of adequate infrastructure and various other catalysts have lead to decentralized greywater reuse efforts both in rural and urban communities. These systems are usually self-implemented and designed for on-site reuse. Treated greywater can be recycled to serve a couple different domestic purposes but the system must be designed specifically to fit source/type of greywater and need. A number of approaches are used to treat water but the most common uses for the final product are irrigation (outdoor) and direct water reuse via sinks and flushing (indoor). Indoor usage requires more intensive water treatment techniques than that of outdoor. Here are descriptions of the general design plan for the most popular systems:

Laundry Drum

Greywater treatment systems span a wide range of complexity. A system can be as simple as diverting used water from your washer to a drum that holds excess^[12]; this is referred to as a “surge tank” (See definition in mechanisms.)A hose attached to the drum can then further divert the water to your crops directly or be hooked to an irrigation system. Because of the nature of the chemical composition of washing machine greywater, treatment is not as necessarily intensive so diverted water can be used directly to water crops (see chemical composition of greywater in introduction).^[13]

Benefits

The benefits of this system are threefold: first is the duality of the washing machine’s built in pump as a mode of washing clothes and a pump source for the greywater system itself; this system is not reliant on gravity. The second benefit is that because of the nature of the greywater source (washing machine) the water does not have to be treated and can be used directly for gardening. Lastly, the plumbing for most washing machine units is exposed providing easy access for diversion if you are a home renter.

Considerations

The largest complication to this sort of greywater system is the dependence of irrigation on the frequency of laundry days.

Laundry-to-Land

Land to laundry (L2L) systems embed the same purpose of the laundry drum (the source/type of greywater and need are the same) and was first designed by Art Ludwig, a greywater activist. Similarly to laundry drums, L2Ls divert used water from washing machine units via a three-way valve connected to the unit. The three-way valve allows for easy diversion of greywater to outside or to the main sewer line, to be used if your garden is becoming overwatered or bleach was added to the laundry load. This feature of the L2L differentiates the system from the laundry drum model. Additionally, the L2L model recommends installation of an anti-siphoning vent on the garden-side of the valve to ensure water is not taken up from the machine while it is filled. (See siphon definition in mechanisms)^[14].

The biggest disparity between the two systems is the L2Ls application of mulch basins as a natural surge tank (see surge tank definition in mechanisms) to release water for irrigation gradually. Mulch is an organic material more commonly referred to as bark, compost or a combination of these that aid in soil insulation and mitigate erosion. Water is diverted via the valve and then directed through a series of underground pipes to these basin, filtering water through and allowing for gradual release of moisture to root systems. The diversion of water to underneath the landscape is another fundamental component of L2Ls. This is preventative of over-saturation that can lead to overwatering and mosquitoes breeding. Piping is usually buried underneath the ground and fed into the mulch basins.

Construction of the mulch basins is simple. It can either consist of a singular large trench or series of trenches that are dug around the vegetation, typically about 12 inches deep and filled with “coarse” mulch (i.e. woodchips).^[15]. The dimensions of the basins should be designed with consideration to the volumetric load they will hold, or the amount of water that will “surge” into the basins. Additional components can be added to aid in treatment processes such as a an outlet chamber. Outlet chambers can be constructed by burying a overturned 5-gallon pot with holes drilled into the sides.^[16] The chamber allows for solids to flow into the basin for biodegradation without clogging over time. This consideration is meant to treat greywater sources that contain solids, or otherwise sources that are not originating from washing machine units (see branched drain in Types.)

Benefits

Mulch basins simulate natural water filtration by serving as an organic surge tank. The suggested three-way valve is a feature that is not included in the laundry drum model and gives the user more control over irrigation frequency. Like the laundry drum model, the intended greywater source is washing machine discharge which does not require intensive treatment but the model can be tailored to fit other sources.

Considerations

Regular maintenance of the mulch basins is required. Designer Ludwig suggests re-digging basins every year or two to counteract erosion.^[17] Additionally, adequate design in regards to mulch basin dimensions are essential to ensure water is effectively filtered to plants.

Branched Drain

This model was also innovated by Art Ludwig, and incorporates the same mulch basin component as an organic surge tank. However, this system is gravity-fed rather than dependent on the internal washing machine pump also allowing for the greywater source not to be limited to this unit. The defining characteristic of branched drain is somewhat self-explanatory; a series of pipes descending in circumference “branch” out from the system’s water source input, allocating an initially large flow of water to smaller outlets. It is recommended that like the L2L model the piping is hidden beneath the landscape, though Ludwig’s design allows for above ground piping system if the user so desires. Subsurface systems are categorically more sanitary and up to code.

Ludwig suggests three methods for “splitting” the flow from the source of greywater. The first mechanism involves the installation of “double ell” attachments which split pipes outlets in two, allowing water to be diverted into different pipes. A branched network can be created with these attachments so that smaller amounts of water are delivered to the necessary places. The second mechanism suggests leaving the water sources separated initially; that is creating separate piping systems for each source input, i.e. kitchen sinks, washing machine, bathroom sink and shower. The third mechanism simply suggests manually moving outlets so that no area becomes too over watered. A combination of all three of these can be constructed in order to fit the specific needs of your system.^[18]

Benefits

Branched drain systems are primarily suited for property that is situated on some type of grade. The larger the degradation the more easy the installation process. This can either be beneficial or an impediment, depending on the nature of the property. This system is open to design interpretation and specialization because the amount of irrigation outlets should be based on the volume of greywater discharged. It can therefore be tailored to fit the needs of any specific property. This also alleviates over-watering because large surges of water can be distributed via branched diversion, delivering smaller amounts to the desired areas.

Considerations

Because this system is gravity fed it must be constructed so that the water is diverted downhill. This system cannot accommodate to uphill irrigation, without the supplementation of a pump. At least a 2% grade (¼” per foot) must exist in order for proper water flow and the pipes must be sloped to exact tolerance. That is, pipes must be installed so that they create a continuous, downhill conduit or else the system may not function correctly.^[19] Additionally, all the considerations pertaining to mulch basin maintenance (see considerations for Land-to-Laundry systems) apply to this system as well as these are an essential component to filtration.

Constructed Wetlands

A constructed wetland (CW) or artificial wetland is a system inspired by the natural biological processes that are occur in wetland ecosystems. CWs can be categorically broken down into three different basic designs: subsurface, surface and floating treatment wetlands.

Subsurface wetlands simply imply diversion of greywater below surface level, limiting exposure to air. Subsurface wetlands can be further broken down based on diversion pathway: horizontal subsurface CWs allow effluent to pass parallel to the surface, propelled by gravity while vertical subsurface CWs allow for the release of water vertically. ^[20]In vertical systems, the water is technically discharged on surface, first watering the strategically chosen wetland plants. It then penetrates the soil to be filtered through the roots and lastly through the chosen substrate (sand, gravel, etc.) Vertical systems require less area as compared to horizontal systems but effluent must be discharged in intervals to avoid flooding, necessitating the implementation of a surge tank. While horizontal systems require more area, they have a larger capacity for discharge. The wetland systems themselves are comprised of the same basic components: a top layer of soil containing wetland species (preferably native to the area) and a medium of filtration. This medium is typically sand or gravel and serves as a platform for microbial growth and aids in filtration and absorption of greywater.^[21] The bottom is either line with a waterproof synthetic material (such as pond liner or tarp) or organic insulating material such as clay in order to mitigate groundwater contamination.

Surface CWs (also called free-surface CWs) are structurally similar to subsurface systems but differ in that they allow for pooling of effluent. Once the effluent is discharged it slowly flows through a basin, allowing suspended sediment to settle. The water then moves downward and is filtered through the rhizomal network established by the planted wetland species. These networks are supportive of microorganisms which feed on the nitrogen and phosphorous contained in the effluent.^[22] Pathogens are broken via natural decay, predation and exposure to UV radiation. ^[23]This exposure is an important disparity when compared to subsurface mechanisms. However, this exposure also creates a breeding ground for less desirable organisms such as mosquitoes. Suitable vegetation for surface CWs include emergent, submerged and subsurface plants.

Free-floating systems differ in structure drastically when compared to surface and subsurface wetlands. The design mimics some components of hydroponic growth, as organisms are planted on a floating mat or substrate in a pond. The stems of the plants are exposed to air, while the roots intake nutrients directly from the water column. The function of the established rhizomal system itself is the same as in a subsurface or a surface CW, except the network may be more extensive in the absence of a soil medium. The network also forms a microbial biofilm, a thin layer of cells. In this system the roots execute both biological and physical processes of treatment. That is they physically filter and trap particulates while also converting nitrogen and phosphorous via biochemical processes in the biofilm.^[24]

Benefits and Considerations

Constructed wetlands are by far the most complex of the described management systems, with the most room for customization. They are also wide ranging and a number of hybrid systems that incorporate aspects from different designs are used to accommodate specific criteria. The biggest benefit of these systems is their self-sufficiency if installed correctly while perhaps the biggest drawback is the rigorous and involved process of design specialization and implementation.

Summary

The systems described are not representative of the entirety of greywater management approaches but are a summarized list of the most popular, decentralized, “low-tech” systems. Of course more exotic systems have been created such as rotating biological contactors which treat water via UV exposure and sequencing batch reactors which utilize activated sludge technology.^[25] However these systems are not applicable to the layperson and thus not available for self-installation. For this reason they have been excluded from the scope of this review.

Current CCAT Greywater System

As far as we know the most recent update for this project is the 2009 edition. Per Connor Kennedy, the CCAT grounds keeper (2017), this system has been redesigned many times since then.

Design

The current system is a simple design to filter CCAT’s grey water. It starts by coming out of the house and flows through a long pipe that takes it directly to just before the location of the marsh. Here it is dumped into a settling tank that takes out all the sediment and oils that may clog the marsh. From the settling tank the water is directly poured into the marsh where it moves through a baffled filter system. Since there is no direct place for the water to go after it has been fully treated, it ends up just being run off.

Problems

The known problems with the system include level ground, and too much surface area per volume amount of water filtered. To begin, the ground where the pipe is laid is level. This inhibits the water's ability to reach the actual location of the marsh. Finally, the built marsh has too much area to be effective. This current system was not designed with the water use of CCAT in mind. Since CCAT’s residence do not use enough water for the greywater marsh to work properly.

Settling tank

The settling tank is a very simple design, but effective. The settling tanks acts like a sedimentation tank.^[26] A sedimentation tank works by slowing the flow of water, allowing the suspended particles to settle onto the bottom. This collection of waste is called primary sludge^[27], and must be removed manually. The way that this settling tank is designed incorporates an oil filter into it. It is a series of two buckets, the second bucket is smaller than the first so that it can be suspended inside the first bucket. The water comes from a pipe that is attached to the roof of the system and pours through the oil filter and rises back up to the top where it flows through another pipe that leads to the marsh. This allows for the flow of water to stop, giving the suspended solids the ability to sink to the bottom and effectively be filtered out of the water.

Oil filter

The primary objective of an oil filter is to remove any oils that may be in the water. The reason for this is so that any part of the entire marsh system does not become clogged. The oil filter is a part of the sediment tank design. This is simply a wire mesh sheet attached to the first bucket described above. This essentially acts as a screen^[28] that traps and captures the oil. The oil is further filtered through the sedimentation trap part of the settling tank and settles to the bottom becoming primary sludge.

Baffled system

A baffled filtering system includes a series of up – flow chambers.^[29] The water initially enters a sediment tank. Then, as the water level goes up it overflows into a separate tank where it penetrates through the soil and back up into the same type of overflow tank as the first. It repeats this process until the water is fully filtered. This system is not effective with weakly polluted water, but is hard to clog.^[30]

Surge Tank

A surge tank is a storage reservoir that is on the downstream end of a water source that mitigates sudden bursts in water flow.^[31] Surge tanks are very helpful in systems where the grey water is being treated. This initial tank stores water and allows for an even flow of water to the next stage in the process. This stops flooding to certain parts of the system that takes longer, like filters and pumps.^[32]

Siphon

A siphon is a tube or pipe that is used to transfer water from one reservoir to another, on a lower level, without the use of a pump. Siphons contain steady flow using suction or immersion. An example of this would be a dosing siphon, where it uses suction, gained from breaking a vacuum, to obtain a constant flow.^[33]

Pumping

While many systems will be gravity fed, there is still the case where one would need to pump the water. This may be the case in a situation with the filtration system being uphill from the initial output. This can be done with a general water pump, and is the easiest method for such scenarios. Unfortunately, this does not mean it is the most efficient.

Project Criteria

Talking with the CCAT client we came up with a set of criteria. Each criteria will have its own constraints and is ranked with a 0-10 scale, where 0 is not important and 10 is most important.

References

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