Patent Publication Number: US-2023132622-A1

Title: Greywater treatment system

Description:
FIELD OF THE DISCLOSURE 
     The disclosure relates to greywater treatment systems and more specifically to modular greywater treatment systems including two-stage filtration. 
     BACKGROUND 
     As human population increases, ever greater demands are being put on natural resources. Food production and energy production systems are being taxed, resulting in food and power shortages. Another natural resource that is becoming scarce is safe fresh water. Water shortages have been experienced worldwide in recent years as population centers exhaust their supplies of fresh water. Water shortages have a destabilizing effect on local economies and may even lead to national or international conflicts. 
     Approximately 80% of the world’s population lives in areas having vulnerable water supplies. Excessive human water use can detrimentally affect wildlife, such as migrating fish, and can cause depletion of fresh water sources. Furthermore, dense population centers require extensive water delivery infrastructure. Good management of fresh water resources can protect wildlife while increasing water security. 
     Increases in population can result in water crises during droughts when water demand exceeds natural water replenishment of fresh water supplies. Generally, rainfall comes from complicated internal processes in the atmosphere that are very hard to predict. As population increases, naturally occurring periods of lower rainfall may result in water shortages as demand exceeds supply. 
     Although an overwhelming majority of the planet surface is composed of water, 97% of this water is saltwater. The fresh water used to sustain humans is only 3% of the total amount of water on Earth’s surface. Therefore, there is a limited supply of fresh water, which is stored in aquifers, in surface reservoirs and in the atmosphere. While seawater may be desalinated to render the water potable or useable by humans, only a very small fraction of the world’s water supply derives from desalination because desalination is an expensive, energy intensive process. 
     Fresh water supplies may be better managed through conservation efforts, such as water reclamation and water recycling. In some cases, demand on fresh water supplies may be reduced by reclaiming water that would otherwise go unused. One reclamation process is collecting rainwater in containers and storing the collected rainwater for later use. Water recycling, on the other hand, may be used by virtually any population, even those located in areas that receive little rainfall. Water recycling includes reusing or repurposing water that is used during human activities. 
     Generally, daily human water use produces two categories of wastewater, which are known as “greywater” and “blackwater.” Blackwater is wastewater that includes biological waste, such as feces and urine or is water heavily loaded with other contaminants such as food waste or wash water discharge from the wash cycle of a clothes washing machine. Blackwater is produced by toilets and other human waste collectors and requires extensive treatment before being released back into the environment due to its high organic content, dissolved solids, and contamination by various pathogens. Greywater, which is generated from domestic activities such as the rinse cycle of clothes washing machines, lavatory use, and bathing, requires less treatment as greywater generally contains fewer organic compounds than blackwater and generally includes less pathogen contamination. Greywater is produced by lavatory sinks, showers, the rinse cycle of clothes washing machines, and some industrial light use processes, etc. 
     Greywater may be used for many purposes that would otherwise use fresh, potable water. For example, greywater may be used for flushing toilets and irrigating outdoor plants. Using treated greywater to flush toilets, for example, instead of using fresh, potable water, can reduce the daily use of fresh, potable water by up to 30% in a typical family home. 
     As demands for potable water increase, communities will rely more heavily on water conservation efforts that include water recycling. Greywater recycling may become a key component of a water recycling system. In fact, some governments are incentivizing water conservation efforts by legislating tax breaks for programs that result in a reduction in fresh potable water usage from the community water supply. Recycling or repurposing greywater is often one component of such programs. 
     Current greywater recovery systems are generally limited to repurposing untreated greywater for irrigation purposes. Such systems are relatively simple, only requiring a separation of the greywater from the blackwater before the two are mixed. Then, the greywater is diverted outside for irrigation. These systems require that any irrigation be done through subsurface methods to minimize risks to public health and such systems are generally prohibited from storing greywater for extended periods. Most current greywater recovery systems do not treat greywater for indoor reuse. 
     Untreated greywater is heavily regulated by local health regulations, which generally restrict the uses for untreated greywater due to potential public health issues. In many localities, contact of untreated greywater with humans is prohibited and thus, using untreated greywater for indoor or above ground irrigation use is not currently allowed in most countries. 
     SUMMARY 
     According to a first embodiment, a greywater treatment system includes a first modular greywater processing apparatus having a raw greywater inlet, a mechanical (MTF) filter connected to the raw greywater inlet, and a first ultrafine (UF) filter connected in series downstream of the mechanical filter. The UF filter includes a UF filter inlet, a filtrate outlet, and a cross-flow outlet. The filtrate outlet is connected to a processed water outlet. A modular base supports the mechanical filter and the UF filter. 
     The foregoing first embodiment of a greywater treatment system may further include any one or more of the following optional features, structures, and/or forms. 
     In some optional forms, a second UF filter is connected in parallel with the first UF filter, and in series with mechanical filter. 
     In some optional forms, the mechanical filter filters out particulate matter 200 microns or larger. 
     In some optional forms, the mechanical filter includes a backwash outlet that is adapted to be fluidly connected to a sewer. 
     In some optional forms, a differential pressure monitor is connected to the mechanical filter. 
     In some optional forms, a first control valve is disposed between mechanical filter and the UF filter. 
     In some optional forms, the filtrate outlet is fluidly connected to a processed water holding tank. 
     In some optional forms, the cross-flow outlet is fluidly connected to a raw greywater tank. 
     In some optional forms, an ultraviolet (UV) sterilizer is disposed downstream of the UF filter. 
     In some optional forms, a backwash line is disposed between the UV sterilizer and the UF filter. 
     In some optional forms, the UF filter removes particulates 0.02 microns and larger. 
     In some optional forms, a first backwash valve is disposed downstream of the UF filtrate outlet. 
     In some optional forms, a first control valve is disposed between the MTF filter and the UF filter. 
     In some optional forms, a second control valve is disposed downstream of the UF filtrate outlet. 
     In some optional forms, a third control valve is disposed between the UV sterilizer and the UF filtrate outlet. 
     In some optional forms, a second modular greywater processing apparatus is operatively connected to the first modular greywater processing apparatus. 
     In some optional forms, the second modular greywater processing apparatus includes a third UF filter connected in parallel to a fourth UF filter, both the third UF filter and the fourth UF filter being connected in series to the mechanical filter. 
     In some optional forms, a third modular greywater processing apparatus is operatively connected to the second modular greywater processing apparatus. 
     In some optional forms, the third modular greywater processing apparatus includes a fifth UF filter connected in parallel to a sixth UF filter, both the fifth UF filter and the sixth UF filter being connected in series to the mechanical filter. 
     In some optional forms, a chemical backwash system is fluidly connected to the UF filter. 
     In some optional forms, the chemical backwash system comprises a mixing tank and a chemical supply. 
     In some optional forms, the chemical backwash system further comprises a mixing venturi upstream of a chemical supply inlet. 
     In some optional forms, the mixing tank comprises a processed greywater inlet. 
     According to a second embodiment, a method of operating a greywater treatment system includes backwashing an MTF filter and a UF filter based on a zero flow reading from a flow sensor for a minimum period of time, and emptying raw greywater from a raw greywater tank. 
     The foregoing second embodiment of a method of operating a greywater treatment system may further include any one or more of the following optional features, structures, and/or forms. 
     In some optional forms, the minimum period of time is between 16 and 24 hours, preferably about 18 hours. 
     In some optional forms, the flow sensor is disposed downstream of the UF filter. 
     In some optional forms, the UF filter is continuously cleaned with a crossflow circuit and the waste from the crossflow circuit is returned to the raw greywater tank or to a sewer. 
     In some optional forms, the UF filter is backwashed based on a minimum flow input from the flow sensor. 
     In some optional forms, the minimum flow reading is between 1000 gallons of processed water and 3000 gallons of processed water, preferably between 1500 gallons of processed water and 2500 gallons of processed water, and more preferably at approximately 2000 gallons of processed water. 
     In some optional forms, the MTF filter is backwashed based on one of a maximum differential pressure input from a pressure sensor and a minimum flow input from the flow sensor. 
     In some optional forms, the maximum differential pressure is between 0 psi and 10 psi. 
     In some optional forms, the minimum flow input is between 35 gallons per minute and 80 gallons per minute 
     In some optional forms, the UF filter is chemically backwashed with a high pH solution based on a minimum flow input from the flow sensor. 
     In some optional forms, the minimum flow input for the chemical backwash is between 30,000 gallons of processed water and 50,000 gallons of processed water, preferably about 40,000 gallons of processed water. 
     In some optional forms, a processed water backwash is completed after the chemical backwash. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter, which is regarded as forming the present invention, the invention will be better understood from the following description taken in conjunction with the accompanying drawings. 
         FIG.  1    is a perspective view of a first modular greywater processing apparatus. 
         FIG.  2    is front planar view of the modular greywater processing apparatus of  FIG.  1   . 
         FIG.  3    is rear planar view of the modular greywater processing apparatus of  FIG.  1   . 
         FIG.  4    is a first side view of the modular greywater processing apparatus of  FIG.  1   . 
         FIG.  5    is a second side view of the modular greywater processing apparatus of  FIG.  1     
         FIG.  6    is a schematic illustration of a greywater treatment system including the modular greywater processing apparatus of  FIG.  1   . 
         FIG.  7    is a schematic illustration of the modular greywater processing apparatus of  FIGS.  1  and  6   . 
         FIG.  8    is a schematic illustration of a raw greywater holding tank of the greywater treatment system of  FIG.  6   . 
         FIG.  9    is a schematic illustration of a chemical backwash supply module of the greywater treatment system of  FIG.  6   . 
         FIG.  10    is a schematic illustration of an ultraviolet treatment module of the greywater treatment system of  FIG.  6   . 
         FIG.  11    is a schematic illustration of a processed water holding tank of the greywater treatment system of  FIG.  6   . 
         FIG.  12    is a perspective view of an alternate embodiment of a modular greywater processing apparatus having a second UF filter. 
         FIG.  13    is a perspective view of two alternate modular greywater processing apparatus of  FIG.  12    connected to one another in parallel. 
         FIG.  14    is a perspective view of three alternate greywater processing apparatus of  FIG.  12    connected to one another in parallel. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosed greywater treatment systems generally collect greywater from a greywater source, such as sinks, showers, or the rinse cycle of clothes washing machines, the systems then treat and store the greywater and distribute the treated greywater for reuse. The treated greywater may be used indoors, for example, to flush toilets, thereby reducing consumption of potable fresh water. The treated greywater may be used for other purposes, such as for water in clothes washing machines, or for above-ground spray irrigation systems, and some light industrial processes. 
     The benefits of collecting or harvesting greywater, treating the collected greywater, and reusing the treated greywater go far beyond fulfilling a desire to be “green.” Collecting, treating, and reusing greywater can have lasting economic benefits for building owners and for communities in general. By reusing treated greywater to flush toilets or urinals, to irrigate landscaping, or to support other water-intensive operations, municipal water charges can be significantly reduced. Wastewater treatment fees and environmental impact fees can also be reduced. Additionally, large scale reuse of greywater may stretch supplies of potable freshwater for communities, which extends the natural resource of water while simultaneously reducing individual water costs. 
     In high density buildings, the greywater treatment and reuse systems advantageously provide a relatively constant supply of treated greywater for flushing toilets. In some cases, the supply of treated greywater can meet 100% of toilet flushing requirements for a particular building. Because the disclosed greywater collection and treatment system provide a supply of greywater that is steady and predictable, storage requirements are reduced, saving storage space and cost. In other words, the predictable nature of greywater production in high density buildings allows the disclosed greywater treatment and reuse systems to be tailored in capacity for a particular building so that the supply of treated greywater generated by the greywater treatment and reuse systems closely match the demand for treated greywater (i.e., so that supply virtually matches demand), which reduces the need for extended storage of the treated greywater. Other uses for treated greywater include makeup water for evaporative cooling towers. 
     Greywater (also referred to as grey water, gray water and greywater), as used herein, refers to water that is produced by human domestic operations and that does not include significant concentrations of human biological waste (i.e., urine and feces) or food waste. Greywater is generally produced by sinks, showers, baths and light industrial applications, such as the rinse cycle of clothes washing machines and, and has not yet been treated (e.g., filtered and/or chemically treated) for pathogens. 
     When properly filtered and stored, greywater can be a valuable source of water to flush toilets, to flush urinals, or to irrigate landscaping. Toilet flushes can account for 25-65% or more of the total water use in a commercial building, even when low-flush fixtures are used. 
     Turning now to  FIGS.  1 - 5    a first modular greywater processing apparatus  100  is illustrated. The first modular greywater processing apparatus  100  may be incorporated into a greywater treatment system  10  (not fully illustrated in  FIGS.  1 - 5   , but schematically illustrated in  FIG.  6   ), which will be discussed further below with respect to  FIGS.  6 - 11   . The first modular greywater processing apparatus  100  comprises a raw greywater inlet  120  that is fluidly connected to a mechanical (MTF) filter  122 . A first ultrafine (UF) filter  124  is fluidly connected in series downstream of the mechanical filter  122 . The UF filter  124  includes a UF filter inlet  126 , a filtrate outlet  128 , and a cross-flow outlet  130 . The filtrate outlet  128  is connected to a processed water outlet  132 . A backwash inlet  133  is connected to the filtrate outlet  128  for use during backwash (cleaning) operations. A modular base, such as a skid  134 , supports the MTF filter  122  and the UF filter  124 . 
     The MTF filter  122  is a self-cleaning mechanical filter that captures relatively large particulates in the greywater stream. The MTF filter  122  captures particulates larger that about 200 microns, such as lint, hair, and other large debris. The MTF filter  122  includes a backwash outlet  140  that is adapted to be fluidly connected to a sewer (or to a raw greywater holding tank) by a wastewater outlet  142  so that backwash water may be directed to the sewer after a backwash cleaning cycle. A backwash valve  144  opens to allow backwash water to flow to the wastewater outlet  142  during the backwash cycle, which will be discussed further below. A differential pressure monitor  146  ( FIG.  7   ) is fluidly connected to the MTF filter  122  and the differential pressure monitor  146  measures differential pressure across the MTF filter  122  and sends the measurements to a MTF controller  190 . The MTF controller  190  uses the differential pressure measurements to determine if the MTF filter  122  needs to be cleaned through a backwash cycle as the differential pressure across the MTF filter  122  is an indication of a saturation level of the MTF filter  122  with filtered particulates. The MTF filter  122  may be backwashed based on a time interval, or based on the measurements from the differential pressure monitor  146 . In some embodiments, the maximum differential pressure is between 0 psi and 10 psi, preferably between 3 psi and 10 psi, and more preferably between 5 psi and 9 psi. In some embodiments, the minimum flow input is between 35 gpm and 80 gpm, preferably between 45 gpm and 70 gpm per membrane. 
     A first backwash valve  170  is disposed between the MTF filter  122  and the UF filter  124 . The first backwash valve  170  directs backwash water from the MTF filter  122  to the wastewater outlet  142  during a backwash cycle. 
     The UF filter  124  is an ultrafine membrane filter with a cross-flow cleaning circuit. The ultrafine membrane filter comprises both flat sheet and capillary membranes. The UF filter  124  removes particulates 0.02 microns and larger, which includes pathogens (such as bacteria and viruses) and suspended solids. In some embodiments, a second UF filter  125  may be connected in parallel with the first UF filter  124  and in series with the MTF filter  122 , as illustrated in  FIG.  12   . The UF filter  124  may be continuously cleaned by a crossflow circuit and waste from the crossflow circuit may be returned to a raw greywater tank or to a sewer. 
     Turning now to  FIG.  6   , a greywater treatment system  10  is illustrated that includes the modular greywater processing apparatus  100  if  FIGS.  1 - 5    (or of  FIG.  12   ). The greywater treatment system  10  comprises a raw greywater holding tank  200  fluidly connected to the modular greywater processing apparatus  100  so that raw greywater may be pumped from the raw greywater holding tank  200  to the modular greywater processing apparatus  100 . After filtering in the modular greywater processing apparatus  100 , the filtered greywater is pumped to an ultraviolet (UV) sterilization unit  300  that is downstream of the UF filter  124 . After sterilization in the UV sterilization unit  300 , the sterilized greywater is pumped to a processed greywater holding tank  400 . A chemical backwash unit  500  supplies chemical backwash fluid to the modular greywater processing apparatus  100  at regular intervals (or on demand) to clean the MTF filter  122  and the UF filter  124 . 
     The raw greywater holding hank  200  is fluidly connected to sources of greywater, such as plumbing fixtures, washing machines, etc., by a raw greywater inlet line  202 , which directs raw greywater into a raw greywater tank body  204 . The raw greywater tank body  204  includes a raw greywater pump  206  that pumps raw greywater out of the raw greywater tank body  204  through a raw greywater output line  208 , which leads to the MTF filter  122 . The cross-flow outlet  130  from the UF filter  124  is connected to an internal cross-flow circuit (not shown) that continuously removes loading from the membrane and returns the loading to the raw greywater holding tank  202  through a cross-flow line  158 . 
     From the MTF filter  122 , the filtered greywater flows to the UF filter  124  through a mechanical filtrate line  160 . After passing through the UF filter  124 , the filtered greywater exits the UF filter  124  through a filtrate line  162  to a UV sterilizer  302 . After sterilization in the UV sterilizer  302 , the sterilized greywater is directed to a processed water tank body  402  in the processed water holding tank  400 . In embodiments without a UV sterilizer  302 , the filtrate outlet  132  may be directly fluidly connected to the processed water holding tank  400 . A processed water pump  404  pumps the processed water from the processed water tank body  402  to downstream users of the processed water through a processed water exit line  406 . 
     A processed backwash pump  408 , which is activated during a standard backwash cycle, pumps processed water through backwash line  410 , part of which connects the UF filter  124  to the UV sterilizer  302 , to clean the UF filter  124 , the MTF filter  122 , and the UV sterilizer  302  during a standard backwash cycle. Generally, the standard backwash cycle is initiated after about 2000 gallons of greywater have been processed by the UF filter  124 , although in other embodiments, other thresholds of processed greywater may be used to initiate the standard backwash cycle. The standard backwash cycle may also be initiated as a function of differential pressure across the MTF filter  122 . 
     When more thorough cleaning is needed, the chemical backwash unit  500  supplies a chemically enhanced cleaning solution (normally a high pH solution) through a cleaning line  502  to the UF filter  124  during a chemical backwash cycle. The chemical backwash cycle is normally initiated after about 40,000 gallons of greywater have been processed by the UF filter  124 , although in other embodiments, other thresholds of processed greywater may be used to initiate the chemical backwash cycle. 
     The backwash operations are controlled by the first backwash valve  170  disposed downstream of the UF filtrate outlet  128 , a first control valve  172  disposed upstream of the raw greywater inlet  120 , a second control valve  174  disposed downstream of the UF filtrate outlet  128 , and upstream of the first backwash valve  170 , and a third control valve  176  disposed between the UV treatment apparatus  302  and the UF filtrate outlet  128 . The first, second, and third control valves  172 ,  174 ,  176 , in the illustrated embodiment, are three-way motorized valves. The first backwash valve  170 , in the illustrated embodiment, is a solenoid valve. 
     In the embodiments illustrated in  FIGS.  12 - 14   , the description of the UF filter  124  in the paragraphs above applies equally to any UF filter described below. Any feature of the UF filter  124  in the paragraphs above may equally be incorporated in the UF filters described below. 
     The modular nature of the modular greywater processing apparatus  100 , enables multiple modular greywater processing apparatus  100  to be connected in parallel to one another so that the greywater treatment system  10  may be scaled appropriately for the needs of a particular project. For example, turning now to  FIG.  13   , in an alternate embodiment, a second modular greywater processing apparatus  100   a  may be connected in parallel to the first modular greywater processing apparatus  100 . The second modular greywater processing apparatus  100   a  comprises a third UF filter  127  connected in parallel to a fourth UF filter  129 , and both the third UF filter  127  and the fourth UF filter  129  are connected in series to the mechanical filter  122 . 
     Turning now to  FIG.  14   , in another alternate embodiment, a third modular greywater processing apparatus 100b may be connected in parallel to the first modular greywater processing apparatus  100  and to the second modular greywater processing apparatus  100   a . The third modular greywater processing apparatus  101   b  comprises a fifth UF filter  131  connected in parallel to a sixth UF filter  133 , and both the fifth UF filter  131  and the sixth UF filter  133  are connected in series to the mechanical filter  122 . Each modular greywater apparatus (i.e., each pair of UF filters) increases overall system capacity by approximately 70 gpm. Each modular greywater processing apparatus  100  may be pre-wired and transported to a use location separately. Once located at the use location, the modular greywater apparatus  100  may be quickly connected to one another in the field. 
     Turning now to  FIG.  9   , the chemical backwash unit  500  comprises a mixing tank  504  and a chemical supply. The chemical supply in the illustrated embodiment comprises a first chemical supply  506  and a second chemical supply  508 . The first chemical supply  506  may be connected to a first chemical inlet  510  and the second chemical supply  508  may be connected to a second chemical inlet  512 . In one embodiment, the first chemical supply  506  may comprise NaOH and the second chemical supply  508  may comprise NaOCL. In other embodiments, other chemicals may be used. The first and second chemicals are injected into the mixing tank  504  through a mixing venturi  510  downstream of the first and second chemical inlets  510 ,  512 . More specifically, in the illustrated embodiment, a chemical backwash pump  514  circulates a chemical backwash fluid from the mixing tank  504 , which may also be referred to as a chemical backwash tank  516 , through a circuit  520 . As the chemical backwash fluid circulates in the circuit  520 , the first and second chemicals are added to the circuit  520  through the first chemical inlet  510  and the second chemical inlet  512 . Chemicals are added and the chemical backwash fluid is circulated until a desired concentration of the first and second chemicals is reached in the chemical backwash fluid in the chemical backwash tank  516 . The circuit  520  is controlled by a chemical backwash control valve  530 . When the chemical backwash cycle is activated, the chemical backwash control valve  530  moves to direct the chemical backwash fluid from the chemical backwash tank  516 , through a first branch 520a of the circuit  520  and into the cleaning line  502  for delivery to the UF filter  124 . The chemical backwash tank  516  derives make up water from the processed water holding tank  400  through a processed water makeup line  534  that empties into a processed greywater inlet  532 . 
     Normal Operation 
     Returning now to  FIG.  6   , during normal operation, raw greywater is pumped from the raw greywater holding tank  204  to the modular greywater processing apparatus  100  at a rate of between 30 and 220 gpm at approximately 40-65 PSI, through the raw greywater output line  208 . The raw greywater enters the MTF filter  122 , where it passes through a 200 micron screen. The MTF filter  122  removes large particles, such as hair, lint, and larger debris. From the MTF filter  122 , the greywater enters the UF filter  124  through the raw greywater inlet  120 . After exiting the UF filter  124 , the filtered greywater is delivered to the UV sterilizer  302  through the filtrate line  162 . After exiting the UV sterilizer  302 , the sterilized greywater is delivered to the processed water holding tank  400  through a processed water line  330 . During normal operation, the first backwash valve  170  is open and the first control valve  172  is in a process position, allowing greywater to flow from the MTF filter  122  to the UF filter  124 . The second control valve  174  is in a process position, allowing the filtered greywater to flow from the UF filter  124  to the UV sterilizer  302 , and the third control valve  176  is in a process position, allowing the filtered greywater to flow from the UF filter  124  to the UV sterilizer  302 . 
     Standard Backwash Cycle 
     As discussed above, the standard backwash cycle is initiated after about 1000-3000 gallons, preferably between about 1500 and about 2500 gallons, and more preferably between about 1500-2000 gallons of greywater have been processed by the UF filter  124 . Greywater flow through the UF filter  124  is monitored by a flow transmitter  180  connected to the filtrate line  162 . The standard backwash cycle keeps the membranes in the UF filter  124  relatively clean so that they operate at optimum levels. Operation of the greywater treatment system  10  is controlled by the controller  600  that is normally disposed on the modular greywater processing apparatus  100 . Although electrical connections between the controller  600  and various components of the greywater treatment system  10  are not illustrated, where the controller  600  is discussed as communicating with a component, such as a control valve, the controller  600  is communicatively connected to that component. The communicative connections may be electrical connections, pneumatic connections, or wireless connections, or any other type of connection that allows communication between the controller  600  and the various components of the system. During the normal backwash cycle, the first backwash valve  170  is closed, preventing fluid flow between the UF filter  124  and the UV sterilizer  302  through the filtrate line  162 , the first control valve  172  is in a drain position, which allows backwash fluid (which is taken from the processed water holding tank  400 ) to flow out of the UF filter  124  through the raw greywater inlet  120  to a sewer (or to the raw greywater holding tank  202 ), and the second control valve  174  and the third control valve are in a normal backwash position, which allows backwash fluid to flow from the processed water holding tank  402  through the backwash line  410  to the filtrate outlet  128  so that the UF filter  124  is backwashed. The normal backwash cycle is between approximately 30 and 120 seconds long, preferably between 40 and 100 seconds long, more preferably approximately 45 seconds long. In some embodiments, the length of the backwash cycle may be adjustable to account for differing cleaning requirements. 
     Chemical Backwash Cycle 
     The chemical backwash cycle is activated after between approximately 30,000 gallons and 100,000 gallons, preferably between about 30,000 and 50,000, and more preferably about 40,000 gallons, of greywater have been processed by the UF filter  124 . Similar to the normal backwash cycle, greywater flow through the UF filter  124  is monitored by the flow transmitter  180 . The purpose of the chemical backwash is to circulate a high pH solution of NaOCL and NaOH the UF Filter  124  to remove scale and/or to kill any biological agents that may have collected on the UF filter  124  membranes. The chemical backwash cycle lasts between 4 and 10 minutes, preferably between 4 and 8 minutes, and more preferably about 5 minutes. During the chemical backwash cycle, the chemical backwash pump  514  is activated to pump chemical backwash solution from the chemical backwash tank  516  through the chemical backwash line  502 . The first backwash valve  170  is closed, the first control valve  172  is in a chemical backwash position in which chemical backwash fluid is directed from the chemical backwash line  502  into the raw greywater inlet  120 . The second control valve  174  is in a chemical backwash position in which chemical backwash fluid is directed from the filtrate outlet  128  to the chemical backwash tank  516  through a chemical backwash return line  550 . The raw greywater pump  206  and the processed backwash pump  408  are off during the chemical backwash cycle. 
     After the chemical backwash cycle is complete, a standard backwash cycle is activated, as outlined above, to remove any traces of the chemical backwash fluid from the UF filter  124  and the flow lines. 
     Automatic Shutdown 
     As described above, the modular greywater processing apparatus  100  must be properly shutdown after use so that any remaining greywater inside the filters and piping doesn’t become blackwater. There are two ways to initiate a full system shutdown. First, the full system shutdown may be manually initiated by a button on a control touchscreen that will start an automatic shutdown sequence. Second, if the flow sensor  180  that monitors the volume of processed water does not see any change over a programmable time period (typically set to 18 hours), the system will automatically force a shutdown sequence if the shutdown push button had not been previously manually activated. 
     In either shutdown instance, the system performs a standard backwash of both the MTF Filter  122  and the UF Filter  124 . Additionally, a drain pump  220  on the raw greywater tank  204  may be activated to empty the raw greywater holding tank  202  to a sanitary sewer at least once per every 24 hours. The automatic shutdown sequence is based on a zero flow reading from the flow sensor  180  for a minimum period of time, such as every 18 hours. In some embodiments, the minimum period of time is between 16 and 24 hours. 
     The disclosed greywater treatment systems have been tested to advantageously produce excellent water quality, which meets or exceeds the NSF  350  standards as listed below in table 1. In most cases, turbidity will be less than 0.5 NTU with 0 levels of E.coli and CBOD and crystal clear water with less than 1 ppm of Total Suspended Solids. Turbidity is measured at various locations throughout the system, for example in the filtrate line  162 . 
     
       
         
          TABLE 1
           
               
               
               
             
               
                 NSF/ANSI 350 STANDARD 
               
               
                   
                 MAX 
                 AVG 
               
             
            
               
                 Turbidity 
                 5 
                 2 
               
               
                 TSS 
                 30 
                 10 
               
               
                 CBOD 
                 25 
                 10 
               
               
                 E. coli 
                 200 
                 2.2 
               
               
                 Odor 
                 Non-Offensive 
               
               
                 pH 
                 6.0-9.0 
               
            
           
         
       
     
     The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.” Moreover, any dimension disclosed in one embodiment is equally applicable in other embodiments. 
     Every document cited herein, including any cross referenced or related patent or application and any patent application or patent to which this application claims priority or benefit thereof, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.