Abstract:
Wastewater can be treated using a combination of a settleable solids separator, such as a vortex separator and a membrane separation system. Removal and segregation of materials that adversely affect operation of the membrane separator earlier in the treatment process can improve water throughput, water quality and the lifespan of system components. Physical separation of settleable solids and floatable materials from the wastewater prior to treatment with a membrane separator can allow higher flow rates to be achieved.

Description:
TECHNICAL FIELD 
     This invention relates to a process and apparatus for treating wastewater. 
     BACKGROUND 
     Declining water tables, population growth, increasing industrialization, expanding use of irrigated agriculture, and pollution of fresh water supplies strain limited fresh water supplies around the world. Reclaimed wastewater can serve as a supplemental source of water, particularly for non-potable uses. Irrigation of crops and landscaping, which constitutes approximately 70% of total water demand and which also benefits from some of the nutrients present in wastewater, represents one suitable non-potable use for reclaimed water. Other appropriate non-potable applications for reclaimed wastewater include washing, cooling, fire prevention and control, creek enhancement, recreational ponds, cement preparation, dust control, and toilet flushing. Despite the wide range of non-potable uses, wastewater reclamation typically has been practiced only on a very small scale. Conveyance of reclaimed water from the reclamation site to a site of use and limited production methods can represent obstacles to more widespread use of reclaimed water. 
     Effective and efficient treatment of wastewater is economically and environmentally important. Wastewater treatment systems can include incineration systems, chemical treatment systems, electrolysis systems, nuclear radiation systems, and physical treatment systems. These various systems can provide water of varying quality. Many of theses systems can be costly and relatively difficult to run and maintain. Physical treatment systems such as filtration can be difficult to develop because of fouling problems and retarded flow. In addition to chemical and pathogenic impurities, incoming wastewater can include settleable solids, such as hard and abrasive materials, that can damage components of the treatment system and floatable materials, such as fats, oils, greases and fibers that can foul a physical treatment system. Useful systems for wastewater treatment can provide consistent output, be capable of automation, be relatively small in size, provide usable liquid and solid byproducts, and be relatively low in cost. 
     SUMMARY 
     In general, the invention features a process and apparatus for treating wastewater streams into beneficial water and solids components using membrane separation as a principal treatment. Removal and segregation of materials that adversely affect operation of the membrane separator earlier in the treatment process can improve water throughput, water quality and the lifespan of system components. Physical separation of settleable solids and floatable materials from the wastewater prior to treatment with a membrane separator can allow higher flow rates to be achieved. 
     In one aspect, the invention features a method for treating wastewater containing settleable solids to form a reusable liquid fraction. The method includes separating a wastewater stream into a first component and a second component in a first containment zone, applying the second component to a membrane permeable to selected ingredients of the second component, and concentrating the second component on a surface of the membrane to form a solids concentrate and a reusable liquid fraction. The first component includes an amount of settleable solids greater than an amount of settleable solids in the second component. The method can include comminuting the wastewater stream prior to separating the first component and the second component. High shear forces can be created between the second component and the membrane. 
     In certain embodiments, separating can also include settling settleable solids by forces generated by wastewater stream flow into a separation tank, by gravity, or by combinations thereof. 
     The reusable liquid fraction can be disinfected. This can be accomplished by, for example, exposing the reusable liquid fraction to ultraviolet radiation. In certain embodiments, disinfecting can include mixing a chemical oxidant, such as ozone, with the reusable liquid fraction. 
     The reusable liquid fraction can be applied to unsaturated soil. The soil can assist in removal and productive reuse of plant nutrients contained in the reusable liquid fraction, and return purified water to underlying aquifers. 
     The method can include removing the solids concentrate from the membrane as a slurry fraction and returning the slurry fraction to the wastewater stream. The method can include passing the reusable liquid fraction through a filter system either prior to or following membrane separation. The filter system can be backflushed, for example, to create a volume of backflushed material and that can be combined with the slurry fraction. The filter system can include a fixed-film biofilter. Contact with the film of the biofilter can result in removal of remaining suspended solids, nitrification of dissolved and suspended nitrogen compounds, and reduction of other sources of biochemical oxygen demand. The biofilter can be backflushable. 
     The wastewater can be obtained from a sewer. The first component and the froth fraction can be combined to form a slurry stream that can be returned to the sewer downstream of the location from which the wastewater was obtained. In certain embodiments, the slurry stream can be passed into a third containment zone to separate it into a supernatant fraction and a settled fraction. Sufficient retention time in the third containment zone can allow for substantial settling of settleable solids to the bottom of the zone. In the third containment zone, solids can be decomposed by a predominantly anoxic biological process. The supernatant fraction can be returned to the first containment zone or the second containment zone, or passed to an underground leach field. 
     In another aspect, the invention features an apparatus for treating wastewater containing settleable solids. The apparatus includes a settleable solids separator, which includes a vessel having an upper end, a lower end, and an outer wall connecting the upper end and the lower end. The settleable solids separator also includes an inlet directed partially tangentially through the outer wall of the vessel, a first outlet proximate to the upper end of the vessel, and a second outlet proximate to the lower end of the vessel. The apparatus also includes a membrane separation system having an inlet and a permeate outlet. The inlet and the permeate outlet are separated by a membrane. A fluid conduit fluidly connects the first outlet of the settleable solids separator and the inlet of the membrane separation system. The membrane separation system can also include a concentrate port. Motive pressure applied to the membrane separation system inlet can be provided by a feed pump in fluid communication with the inlet. 
     The settleable solids separator can be a vortex separator. The settleable solids separator can also include a vent and overflow port positioned between the first outlet and the upper end of the vessel. The second outlet of the settleable solids separator can be a settled solids outlet in communication with an opening in the base of the vessel for removing solids, which are swept towards the opening by a vortex. 
     In certain embodiments, an equalization vessel, that can have an upper end, a lower end, and an outer wall connecting the upper and lower end, can be included between the first outlet of the settleable solids separator and the inlet of the membrane separation system. The vessel can also include a scum overflow and vent port between the normal liquid level of the vessel and the upper end. The inlet of the equalization vessel can be below the first outlet of the separator. The outlet port of the equalization vessel can be at the lower end. 
     The membrane separator system feed pump can receive as input clarified wastewater provided either directly from the first outlet of the settleable solids separator, or in certain embodiments, from the outlet port of an equalization vessel. The apparatus can also include a filter system, which has an inlet and a filtrate outlet, with the inlet in fluid communication with the feed pump, and the filtrate outlet in fluid communication with the membrane separation system feed inlet. The filter system can be a backflushable filter system, a fixed-film biofilter system, or a backflushable fixed-film biofilter system. The backflushable filter can include filter disks. 
     A permeate conduit can fluidly connect the permeate outlet of the membrane separation system with a disinfection system, which can include an ultraviolet disinfection system or an ozone treatment system, or both. The ozone treatment system can include a closed ozone treatment vessel having an ozone injection region in fluid communication with a permeate flowing region. An ozone transport conduit can fluidly connect a closed atmosphere of the settleable solids separator and the closed ozone treatment vessel. 
     The ultraviolet disinfection system can include one or more clear plastic tubes that are transparent to ultraviolet radiation and through which the reusable liquid fraction passes, ultraviolet lamps surrounding the plastic tubes, and an enclosure containing the assembly of tubes and lamps. The ultraviolet lamp apparatus can produce ozone in the air space surrounding the lamps. The ozone can be extracted from the enclosure, which can serve as an ozone generator. An ozone transport conduit can fluidly connect a closed atmosphere of the settleable solids separator and a closed ozone treatment vessel of the ozone treatment system. Exposure to ultraviolet radiation can directly kill organisms, and if dissolved ozone is contained in the liquid, it can create powerful oxidizing agents that further disinfect, remove odor and color, reduce biochemical oxygen demand of, and oxidize harmful chemical compounds in the liquid. 
     The apparatus can include a wastewater pump, such as a comminuting wastewater pump in fluid communication with the inlet of the settleable solids separator. 
     The apparatus can also include a flow restrictor in fluid communication with the concentrate outlet port of the membrane separation system. The flow restrictor can be used to regulate the flow of the process. Periodically, the flow restrictor can be used to retard flow so as to cause the liquid levels of both the vessel of the settleable solids separator and the equalization vessel to rise beyond the overflow ports of both vessels, thereby forcing accumulated scum layer and other floating material on the surface of the vessels to be discharged into the slurry fraction via a scum overflow and vent port that can be in fluid communication with a slurry fraction conduit. The slurry fraction conduit can be in fluid communication with the second outlet of the settleable solids separator. The outlet of the flow restrictor can be in fluid communication with either the settleable solids separator vessel or an equalization vessel. 
     In particular embodiments, the apparatus can include a solids treatment system. The solids treatment system can include an inlet port and an outlet port. The inlet port can be in fluid communication with the slurry fraction conduit. The solids treatment system can include a vessel with an inlet port in communication with the slurry stream, and an outlet port. The solids treatment system can have a volume sufficient to allow the settleable solids in the slurry stream an opportunity to settle and decompose by, for example, predominantly anoxic biological processes. The outlet port of the solids treatment system can be in fluid communication with the inlet of the settleable solids separator. The outlet port of the solids treatment system can be in fluid communication with the inlet of the gravity separator vessel. 
     In another aspect, the invention features an apparatus for treating wastewater containing settleable solids. The apparatus includes a vortex separator and an ozone treatment system. The vortex separator includes a closed separator vessel having an upper end, a lower end, and an outer wall connecting the upper end and the lower end, an inlet directed partially tangentially through the outer wall near the upper end of the vessel, a first outlet proximate to the upper end of the vessel, and a second outlet proximate to the lower end of the vessel. The ozone treatment system includes a closed ozone treatment vessel having a fluid inlet and an ozone injection region in fluid communication with a fluid flowing region. A fluid conduit fluidly connects the first outlet of the vortex separator to the fluid inlet of the ozone treatment system, and the closed separator vessel and the closed ozone treatment vessel are fluidly connected by an ozone transport conduit. 
     The method offers a simple, reliable, rapid, compact and inexpensive process for obtaining reusable water, which can overcome many of the deficiencies of conventional biological wastewater treatment processes. For example, the apparatus and method performs more reliably and efficiently than paper filter, membrane, or biological systems alone. The apparatus is a complete wastewater reclamation system that, among other things, can minimize conveyance costs, can avoid the use of inherently unreliable and maintenance-intensive wastewater treatments, can overcome certain limitations of past physical or chemical systems, can produce reusable or readily disposed residual byproducts, can be compact, economical, reliable, and odorless, and can produce high quality thoroughly disinfected water appropriate to various reuse applications, such as irrigation and other non-critical reuse applications, washing, cooling and other industrial uses, or aquaculture and for discharge to surface water bodies. The method an apparatus can also create an odorless environment in the surrounding of the apparatus. Accordingly, the wastewater reclamation system can be well suited for on-site or local applications in which the water produced is reused productively in the vicinity of the treatment plant. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic view of a water reclamation system including a solids treatment system. 
     FIG. 2 is a schematic view of a water reclamation system including a return for carrying solid residuals to a sewer. 
     FIG. 3 is a plan view of a separation tank. 
     FIG. 4 is a schematic view of a water reclamation system including an ozone treatment system. 
     FIG. 5 is a schematic view of a permeate treatment system. 
     FIG. 6 is a schematic view of a solids treatment system. 
     Like reference symbols in the various drawings indicate like elements. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1-2, a water reclamation system includes settleable solids separator  32 , such as a vortex separator, equalization and cleaning-in-place vessel  52 , filter system  78 , such as a backflushable filter system, membrane separation system  100 , a permeate treatment system  62 , and solids treatment system  92  (FIG. 1) or sewer  20  (FIG.  2 ). Wastewater  21 , which can contain sanitary and other wastes, collects in underground storage tank  22  (FIG. 1) or wet well  96  (FIG.  2 ). Underground tank  22 , or wet well  96 , contains submersible sewage pump  24 . Preferably, pump  24  is a comminuting pump, such as a chopper pump manufactured by Vaughan Chopper Pumps of Montesano, Wash., which simultaneously chops, or comminutes, larger solids in wastewater  21  into a slurry. The slurry is pumped via conduit  26 , through check valve  28  and into settleable solids separator  32  through inlet port  30  of settleable solids separator  32 . 
     Settleable solids separator  32  includes vessel  10  having upper end  12  connected to lower end  13  by outer wall  14 . First outlet  42  is located in outer wall  14  near upper end  12 . Inlet port  30  is directed partially tangentially through outer wall  14  near upper end  12 . Second outlet  46  is proximate to lower end  13 . Closed atmosphere  40  of separator  32  fluidly communicates with vent and scum overflow port  44  connected to vent and scum overflow conduit  45 . Lower end  13  includes second outlet  46 , which is connected to conduit  49  which includes solids pump  48 . Solids pump  48  can be, for example, a progressing cavity pump available from Monyo Inc. of Springfield, Ohio. Referring to FIG. 1, solids pump  48  and drain valve  47  empty through conduit  45  into solids treatment system  92 , which discharges treated material through output port  94 . Referring to FIG. 2, solids pump  48  and drain valve  47  empty through conduit  45  into sewer  20 . 
     Referring to FIG. 3, inlet  30  of separator  32  is directed to create centrifuigal flow pattern  98  that passes around annular dip plate  34 , spillway  36 , and the top of baffle  38 . Spillway  36  is attached to the inner wall of dip plate  34 . First outlet  42  draws fluid from spillway  36 . Vent and scum overflow port  44  is located to one side of separator  32 . Second outlet  46  is centered in vessel  10 . Annular inner baffle  38 , which flares out in a conical shape as it, approaches second outlet  46 . 
     Referring to FIGS. 1-3, first outlet  42  delivers the contents of spillway  36  to gas floatation separation system  52  via fluid conduit  51 . Referring to FIGS. 1-2 and  4 , equalization and cleaning-in-place vessel  52  receives output of settleable solids separator  32  through inlet port  54 . Inlet port  54  is proximate to upper end  55  of vessel  52 . Vessel  52  has reusable liquid fraction outlet port  56  below inlet port  54  and proximate to lower end  57 . Scum overflow and vent port  60  is positioned toward upper end  55  of vessel  52  above the normal liquid level of vessel  52 , draining to conduit  50 . Outer wall  61  connect end  57  and end  55 . 
     Outlet port  56  is fluidly connected to feed pump  66 . Outlet port  56  is part of a circuit passing through conduit  110  to filter system  78 , and through feed conduit  102  to membrane separation system  100 . Suitable membrane separation systems are available from Komline-Sanderson of Peapack, N.J. and New Logic International of Emeryville, Calif. and are described, for example, in U.S. Pat. Nos. 6,027,656, 4,952,317, 5,014,564 and 5,837,142, each of which is incorporated herein by reference. Concentrate output from membrane separation system  100  passes through concentrate conduit  106 , flow control valve  82 , return conduit  58 , and inlet port  30  of settleable solids separator  32 . Permeate from the permeate outlet of membrane separation system  100  passes through conduit  104  to permeate treatment system  62 . A side stream from feed pump  66  passes through drain valve  105  and conduit  111  to join conduit  80 . When necessary, cleaning solution can be supplied to equalization and cleaning-in-place vessel  52  through conduit  113 . Reusable liquid fraction is discharged from outlet  108 . The separating characteristics of membrane separation system  100  can be used more efficiently because most of the settled and floating solids of the wastewater have been removed by settleable solids separator  32 . 
     Referring to FIG. 2, residual solids are returned to sewer  20 . Wastewater  21  from sewer  20  drains into a wet well  96 , which is at an elevation lower than that of sewer  20 . Rather than employ a separate solids treatment system, settled solids from pump  48 , foam, gas and floatable solids from conduits  45  and  50  and filter backflush from conduit  80  drain back to sewer  20  at points downstream of the entrance to wet well  96 . 
     Referring to FIGS. 4 and 5, permeate outlet conduit  104  of membrane separation system  100  feeds permeate to ozone contacting vessel  86  through inlet port  85 . Vessel  86  is closed with permeate inlet  85  proximate to upper end  89 , a reusable liquid fraction outlet  108  proximate to lower end  91 . Vessel  86  includes circulation outlet  93 , located somewhat below inlet  85 , circulation inlet  95  somewhat above reusable liquid fraction outlet  108 , and a foam and ozone outlet  97  proximate to the upper end of  97  and above a normal operating liquid level of the vessel. Circulation outlet  93  is part of a circuit feeding back to circulation inlet  95  through conduit  74 , circulation pump  111 , gas injector nozzle  70 , ultraviolet disinfection system  84  and conduit  74 . Ozone gas is supplied to gas injector nozzle  70  by ozone generator  76 . Referring to FIG. 4, foam and surplus ozone gas from outlet port  97  can be transmitted via conduit  114  to airspace  40  of settleable solids separator  32 . Referring to FIG. 5, system  62  includes backflushable biofilter system  112  that can be inserted between permeate conduit  104  and ozone contacting vessel  86 . When biofilter system  112  is present, the reusable liquid fraction can be used in applications such as aquaculture or discharge to surface water bodies where it can be important that the nitrogen compounds in the water be nitrified and have a low biochemical oxygen demand. For aquaculture use, the rapid treatment process can preserve heat in the water. Suitable backflushable biofilter systems are described in U.S. Pat. Nos. 5,232,586 and 5,445,740, which are incorporated herein by reference, and include the Bubble Washed Bead Filters and Propeller Washed Bead Filters manufactured by Aquaculture Systems Technologies L.L.C. of Jefferson, La. Biofilter system  112  can be backflushed through conduit  107  into sewer  20  or treatment system  92 . Backflushing of biofilter systems can be accomplished using gravity with compressed air or a motorized propeller to agitate the filter medium and to loosen accumulated material. The frequency of backflushing for the biofilter system can be carried out at a regular operational interval, or can be triggered by an increase in feed backpressure. 
     In operation of the systems of FIGS. 1-3, wastewater  21  entering underground tank  22  or well  96  is pumped via pump  24  through check valve  28  into settleable solids separator  32  through port  30 , where flow is directed tangentially to wall  14 , thereby causing the contents of the separator to slowly circulate. Floatable substances, such as fats, oils and greases, in the wastewater quickly rise along the tank periphery as the contents of the separator circulate, causing them to become trapped predominantly in the annular space between dip plate  34  and wall  14 . Settleable solids, such as grit, sand, stones, razor blades, plastics, and other foreign solid materials, in the wastewater fall to the bottom of separator  32  by circulating along the outer periphery of the separator. As the settleable solids reach the bottom of the separator, they are swept inward by centripetal forces created by the differential velocities of the circulating fluid on the outside of the baffle and the relatively stationary liquid toward the center. Solids reaching the outer inclined surface of baffle  38  gradually slide downward and out onto the conical bottom surface of the tank. Centripetal forces created by the relatively quiescent conditions under baffle  38  sweep settled solids inward and trap them under the baffle. Once trapped inside the baffle, suspended solids slowly agglomerate and settle to the bottom. The settled solids exit the separator through outlet  46 . Liquid relatively free of settleable and floatable solids and containing primarily dissolved and suspended solids rises toward the top of the separator inside of annular dip plate  36 , exiting the separator through spillway  36  and port  42 . The component exiting through port  46  contains a greater amount of settleable solids than the component exiting through port  42 . 
     The fluid component exiting port  42  enters equalization and cleaning-in-place vessel  52  at inlet  54  and is pumped out of vessel  52  by pump  66  through outlet  56  to conduit  110  into filter system  78 . After filter system  78 , the fluid passes through conduit  102  into membrane separation system  100 . Within membrane separation system  100 , a portion of the fluid passes through a membrane and is output as permeate to conduit  104 , while the remainder of the fluid exits system  100  as concentrate through conduit  106 . 
     Flow control valve  82 , sewage pump  24 , circulation pump  66 , and settled solids pump  48 , work in a coordinated manner to control fluid flow rates in the overall system. Under ordinary operating conditions, valve  82  typically is set to match the flow rates into the system through pump  24  so that the liquid levels in vessels  10  and  52  remain stable. One way to control flow rates through valve  82  is by interconnecting it with a float pilot valve in vessel  52 , such as is provided by the model 700-60 float-controlled valve system available from Bermad Control Valves of Anaheim, Calif. Flow is increased through the membrane separation system by increasing feed pressure, which can be altered by restricting the flow through valve  82 . 
     A permeate fraction exits conduit  104  substantially free of suspended, settleable and floatable solids. Various subsequent treatments can be provided by permeate treatment system  62 , which will differ depending on the end use intended for the reusable liquid fraction produced. 
     Filter system  78  removes larger particles that could damage the membranes of membrane separation system  100 , or diminish the flow rates achievable by the system. Several types of filter systems can be selected for filter system  78 . One preferred system is a backflushable filter system that uses a plurality of disk filters, such as disk filtration systems manufactured by Arkal Filtration Systems of Kibbutz Bet Zera, Jordan Valley, Israel, which are capable of filtering out materials as small as  10  microns, provide continuous flow using a plurality of filter modules. Suitable filter systems are described in U.S. Pat. No. 4,655,911, which is incorporated herein by reference. In the system depicted in FIG. 1, a filter porosity of 200 microns or less is desirable to remove particulate materials of concern. The backflushable filter system can use a simple and reliable backflush method that backflushes one filter module at a time, while the modules not being backflushed continue to be available to filter water. An air-assisted backflushing step can produce a low volume of backflush, which can decrease the backflush output of the system. The backflushable filter system can employ an automatic backflush cycle that is triggered when the pressure differential across the component filters exceeds a predetermined value. 
     Over time, suspended and dissolved solids in vessel  52  can become increasingly concentrated, which can foul the membrane of system  100 . Fouling of the membrane can result in higher feed pressure when the permeate flow rate is maintained. When higher pressures are detected by an external control system, a cleaning cycle can be initiated after a predetermined pressure threshold is reached. During the cleaning cycle, the following sequence can be followed: (1) flow to vessel  52  through inlet port  54  is stopped by shutting off pump  24 ; (2) vessel  52  is purged by opening drain valve  105 , and closing valve  82 ; (3) vessel  52  is filled with a cleaning solution, such as, for example, a combination of hot water and lye through input  113 ; (4) valve  82  is opened and  105  is closed; (5) the cleaning solution is passed for a period of time through membrane separation system  100 , with a fraction thereof exiting as permeate and disposed; and (6) valve  82  is closed and valve  105  is opened, causing the cleaning solution to be pumped out of tank  52  through valve  105 , conduit  111  and into sewer  20 . Following the cleaning cycle, the startup sequence can be initiated by closing valve  105  and turning on pump  24  to cause new fluid to be admitted to tank  52  through inlet  54 . 
     During operation of the system, scum layers will develop on the surfaces of the liquid in both vessels  32  and  52 . Scum layers can be purged from the system by periodically closing valve  82  for an interval while leaving input pump  24  running. This causes the liquid levels in both vessels  10  and  52  to rise, and eventually spill over through ports  44  and  60  through conduits  45  and  50  into solids treatment system  92  (FIG. 1) or sewer  20  (FIG.  2 ). Once the scum layers have been purged, valve  82  can be opened again to modulate flow by valve  82  to return the liquid level in tank  52  to the target level. 
     Settled solids pump  48  is turned on and off periodically in coordination with the total flow through the system to meter out controlled amounts of solids residuals to solids treatment system  92  (FIG. 1) or sewer  20  (FIG.  2 ). For the embodiment FIG. 1, the solids are concentrated to a high degree prior to treatment, in the range of 5% solids by weight, to minimize the volumes in need of subsequent treatment. The higher solids contents can be achieved by metering the solids residuals using pump  48 . Normally drain valve  47  is closed, but it can be opened to drain tank  32  quickly. 
     The return of concentrate to settleable solids separator  32  can take advantage of kinetic energy remaining in the concentrate stream to assist in maintaining flow, such as centrifugal flow, in vessel  10 , and thereby improving separation efficiency. This centrifugal action can be maintained even after sewage pump  24  is turned off, thereby helping to confine solids in vessel  10  to the conical-bottomed center section while vessels  52  and  10  are emptying. 
     In operation of the permeate treatment system of FIGS. 4 and 5, permeate contained in ozone contacting vessel  86  is circulated through gas injector  70  and ultraviolet disinfection system  84 , during which time permeate is injected with ozone and subjected to ultraviolet radiation. Ozone gas is carried by the circulating stream into contacting vessel  86  where it rises, contacting new permeate traveling slowly in a counter direction from inlet  85  to outlet  108 . The downward flow of liquid from inlet  85  to outlet  108  opposes the upward flow of bubbles, increasing the duration and extent of liquid-bubble contact. Small ozone bubbles contacting the permeate can oxidize substances in the permeate, thereby disinfecting it, while also removing odor and color. Ultraviolet radiation further disinfects the permeate with direct germicidal radiation, while interaction of the radiation with dissolved ozone creates hydrogen peroxide and free radicals which further disinfect, remove odor and color, and oxidize undesirable dissolved organic substances such as are found in herbicides and insecticides. 
     Settleable solids separator  32  and equalization and cleaning-in-place vessel  52  both can have closed atmospheres. This prevents release of odorous gases to the environment surrounding the system. Additional odor control can be provided by surplus ozone released under pressure to airspace  40  of vessel  10 . This ozone can also permeate interconnecting conduits and solids treatment system  92 . This ozone-containing atmosphere can further reduce odors by, for example, oxidizing H 2 S, mercaptans, and other malodorous or harmful gases in the airspaces. The chemical reactions with the ozone not only deodorizes and destroys these materials, but also consumes excess ozone. The reusable liquid fraction generated by the system can be substantially clear, odorless, colorless, disinfected, and free of suspended solids. The reusable water recovered using the system depicted in FIG. 1 can have beneficial attributes for irrigation, washing and cooling uses. For example, the water can contain organic forms of desirable plant nutrients, including trace minerals and nitrogen in forms such as ammonia, which can then be captured by soil particles and converted slowly into nitrates usable by plants. In addition, the reusable water can contain detergents, which can render heavy clay soils more porous, and hydrogen peroxide created by ozone injection, which can improve the health and activity of plant roots. 
     The treatment process can be relatively rapid. The size of the system can be determined, in part, by the dimensions of vessels  10  and  52 , which can be taller than they are wide, and have relatively small volume. Typical water retention times are approximately 15 minutes in vessel  10 , and 10 minutes in vessel  52 . In comparison, biological treatment systems can have hydraulic retention times between 4 hours and several days. Wastewater can be treated in approximately 30 minutes in surface tanks, which can preserve the heat value of the wastewater, which can be supplemented by the pumping energy added by the equipment. Since municipal wastewater typically has a temperature of 65-70° F., the heat can be released in greenhouses during cold months. In addition, because the systems of FIG. 1-2 and  4  use physical separation methods, intermittent use of the system can be facilitated, for example, when there is need for the water. Systems that use biological purification methods can require more stable operating conditions than physical systems. 
     The system depicted in FIG. 2 can be compact, having a very small footprint, rendering it very practical for potential deployment in developed areas where land is scarce and land prices are high. In addition, because the solids are returned to the sewer, there is a decreased need to concentrate solids to a high degree. Accordingly, pump  48  can be operated with a higher duty cycle than in the system of FIG.  1 . 
     The compact nature of the system, and the low odor and noise emissions of the system, allow it to be sited close to populated areas. As long as there are sewers nearby, the system can be sited near a location where the recycled water is needed, such as, for example, in an urban park or a golf course. The attributes of the system allow lower cost and more practical wastewater reclamation to be achieved. 
     Referring to FIG. 6, solids treatment system  92  includes underground tank  114 , which can resemble a septic tank for treatment of residential wastewater. Tank  114  has an inlet port  116 , baffle  118  and conduit  120  between two containment zones of the tank, and outlet port  122 . Inlet port  116  receives by gravity settled solids, gases, foam, and floatable solids collected in other parts of the system from conduits  45  and  50  and the filter backflush of conduit  80 . Output of tank  114  is conveyed through port  122  back to tank  22 . 
     Operation of solids treatment system  92  can be similar to that of a septic tank. The system can operate as an unheated, unmixed anaerobic digester. By design, solids concentrations of the influent can be up to 50 to 100 times greater than that in a typical septic tank for a single family home. As a result, the retention times in the tank can be increased to allow suspended solids considerable time to agglomerate and settle. If, for example, a typical single family septic tank of 1000 gallons retention were used to treat the sewage of 20 homes, the retention time would be approximately 8 to 16 days. The liquid of tank  114  in the clear space between the settled and scum layers can be returned to tank  22  of the system rather than to a leach field. Such liquid will already have undergone partial decomposition by both facultative and anoxic processes. The fate of certain dissolved materials remaining in the liquid returned from tank  114  to tank  22  will differ depending on the type of filtration used in the system are summarized in Table 1. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Fate with Other 
               
               
                 Type of Dissolved Material 
                 Fate with Biofilter 
                 Types of Filters 
               
               
                   
               
             
             
               
                 Ammonia, urea and other 
                 Nitrified to nitrate 
                 Passed on to output 
               
               
                 organic nitrogen compounds 
                 forms 
                 unchanged 
               
               
                 Carbohydrates 
                 Oxidized to 
                 Passed on to output 
               
               
                   
                 H 2 O and CO 2   
                 unchanged 
               
               
                   
               
             
          
         
       
     
     Ozone gas from airspace  40  of vessel  10  can enter the airspace of solids treatment system  92  to destroy H 2 S, CH 4  and odors. As with a conventional septic tank, grit and other inert residual solids in the tank can be removed and disposed periodically, such as by pump truck. 
     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, although municipal and sanitary wastewater can serve as predominant sources of wastewater, other sources are also suitable, including fish tanks and ponds, livestock feedlots, food processing plants, lakes, rivers and streams. In addition, reverse osmosis can be used as a post treatment to the membrane separation system if water of the highest purity is desired. In embodiments, a grinder assembly can be used with the settled solids pump. Moreover, other solids treatment systems, such as a heated and mixed anaerobic digester or an autothermal thermophillic anaerobic digester (ATAD) can be used.