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Reusing Treated Wastewater in Domestic Housing: the Toronto Healthy House project.

by Rolf Paloheimo 
Creative Communities Research Inc. 
152 Sparkhall Ave. 
Toronto, Ontario, Canada, M4K 1G8
Tel  416 466 5172
Fax 416 466 5173

and Bob LeCraw

Presented at

Disposal Trenches, Pre-treatment and Re-Use of Wastewater Conference 
sponsored by the Waterloo Centre for Groundwater Research and the University of Waterloo 
May 13 1996

Introduction

I am a businessman and home builder. As such it is not my usual practice to address people on engineering concepts. I intend to try to convey the vision that the Toronto Healthy House project embodies as it applies to wastewater treatment. Please excuse me if I am a little too general.

The Toronto Healthy House project came about as a result of a nation-wide competition initiated by Canada Mortgage and Housing Corporation, the Healthy Housing Design Competition. The goal of the competition was, in broad terms, to design healthy and environmentally sensitive dwellings suitable for the next century.

With respect to wastewater, the guidelines emphasized reducing or eliminating water consumption and therefor waste water production, minimizing the use of chlorine or other additives and using passive and low energy methods wherever possible.

There were two winners, one in Vancouver and the Toronto Healthy House. The Toronto House was the only urban entry that proposed on-site wastewater treatment.

The design of the project went through many iterations before construction began. The project now includes two homes, both with three bedrooms plus a den, each on a lot measuring 22.5 feet by 80 feet. These are small lots, even by Toronto standards. Each house provides for its own wastewater treatment and disposal as well as fresh water from a rain water cistern system. Both houses reclaim wastewater and recycle it to toilets, laundry, hose bibs, showers and baths.

One house provides all its own energy, the other provides energy to Hydro when the sun is shining and consumes Hydro energy at other times.

Construction is underway at this moment and are scheduled to be finished this summer. One of the houses will be on display for a period of four months after which it will be home to my family. The other will be sold on the open market.

As a result of this project, I as a builder, have become aware of the need for alternatives to existing on-site wastewater systems and also to large scale collection, treatment and disposal as currently practiced by our cities and towns.

Goals with respect to wastewater treatment

In designing the project we were assisted by Al Townshend of Blue Heron Environmental systems. When designing the system, our goals were the following:

  • To develop a wastewater system that;
  • does not require water disposal outside of a small city lot
  • provides for safe and dependable treatment without high energy use or reliance on chlorine
  • provides a marketable and familiar environment to consumers
  • requires only a reasonable amount of maintenance and professional monitoring, the cost of which should not exceed municipal sewage charges.
  • is cost competitive with servicing costs for new unserviced developments.
  • I hope those goals are impressive, they were certainly difficult to achieve. The main problem was disposal.

    Limits on disposal

    As stated earlier, the lots for the Toronto Healthy House project are extremely small, for wastewater disposal purposes. In addition, the land we ended up buying for the project is on the side of a steep hill of fine sandy silt soil with low permeability. Overall, a very poor candidate site for on site wastewater disposal.

    According to the "Manual of Policy, Procedures and Guidelines for Onsite Sewage systems" by the Ministry of the Environment and Energy of Ontario, here is a scaled representation of the area needed for a conventional septic system with an absorption trench leaching system on soil if it had the properties of the Toronto Healthy House site. Shown beside that in the same scale is the amount of space that each of the lots actually provide for wastewater disposal. A not insignificant problem.

     

    In trying to solve the problem we looked at various solutions. One was treating the water to lower disposal requirements. If conventional flows were treated as in a Class 6 system (an aerobic treatment system such as an RBC) in the same manual the chart would look like this:

     

    Still not workable.

    We then added reduced flows using conserving fixtures. We ended up here;

     

    An improvement, however I understand that it is hard to get conservation included in calculations for approvals due to the risk that future owners will change fixtures and plumbing inside the house. In any case it still wasn't enough.

    If we used a sand filter leaching system (again according to the MOEE manual) the problem became this.

     

    The disposal problem plus the fact that we did not have enough fresh water on site forced us into looking at reclaiming wastewater for reuse. To us the logic is as follows, potable water use as a percentage of total water use is only about 15 or 20 percent depending on how you define potable. If wastewater is reused, disposal amounts can be considered to be equal to the water inputs to the house. In this case that is the same as potable water use as a total. Our required and available disposal areas under this scenario looks like this;

     

    Finally disposal is not a problem. In order to fulfill this objective however, disposal water must equal treated potable water of only 120 litres per day and we must recycle 600 litres of water per day for a total of 720 litres water consumption per day per household.

    Adding area for backup, future changes and to allow us to scale back on the amount of recycling brings us back up to this;

     

    Equal, plus some room for error.

    System description

    The general approach we settled on for this system was to look for highly efficient wastewater systems able to digest biological loading effectively in a small space, followed by a polishing stage, where we sought passive and active assurances of quality, safe and aesthetically pleasing finished water.

    The result was that we asked a wastewater specialist and a drinking water specialist to work together on the system, combining their talents to create a system to digest wastewater effectively and ensure that only safe and pleasing water reaches the bathtub spout or sits in the toilet bowl.

    Although the system is not yet operational, I have great confidence in its ability to deliver safe and aesthetic water to my shower head.

    The overall project goals included self sufficient onsite wastewater treatment, and also, no connection to city water supplies. The result was that we included a rain water cistern system. The details of this system are not vital to this gathering, however they do form part of the overall scheme that we are now building.

    Our system in schematic is roughly like this. We had assistance in developing this project from Al Townshend of Blue Heron Environmental Technology who provided guidance in project management and choosing team members. The system design is a joint effort between Blue Heron, Creative Communities, RAL Engineering, and Waterloo Biofilter Inc.

     

    We chose a rain water cistern system for potable water supply since rain is a less polluted source of raw water as compared to ground water in an urban environment. We had assistance in designing the system from RAL Engineering, who are also supplying us with filters for it. In addition we were assisted by Dr. Don Waller's team at the Technical University of Nova Scotia.

    Wastewater treatment

    Once water has been used it becomes wastewater. In the Toronto Healthy House all wastewater , grey and black is combined and treated together.

    The houses can be viewed as a closed system where the disposal of wastewater must necessarily equal the amount of potable water brought into the house. This is an important design parameter, the definition of what is potable water is crucial for setting the amount of water that must be disposed of in a reclaiming system. The discussion of relative flows exceeds the scope available to me here, however, CMHC has funded a related study and development project to develop a computer model of water reuse and flows. Dr. Don Waller of the Technical University of Nova Scotia (TUNS) are working on the model along with others from TUNS and Chris Gates of R.E.I.C.

    An interesting effect of reuse is that water conservation is less of a factor, and only the use of fresh water is a concern. In the case of the Toronto Healthy Houses fresh water is used at the sinks and the dishwasher. All other fixtures use treated wastewater, therefore increased use of water at fixtures that consume reclaimed water only increases the number of times that wastewater is reused. It does not effect water consumption, per se.

    In addition to disinfection, the proposed wastewater reclamation systems for the Toronto Healthy Houses have four levels of treatment; preliminary, primary, secondary and advanced treatment. The design flow for each house is 720 litres per day consisting of 120 litres per day of waste potable water and 600 litres per day of grey and black water. Each house will have its own dedicated system.

    For this project, preliminary, primary and secondary treatment are provided based on advice, designs and contributions made by Dr. Craig Jowett and Waterloo Biofilter Systems Inc. The problem that we handed Dr. Jowett was roughly this; starting with a combined household wastewater of estimated but unconfirmed quality, to deliver as effluent to disposal and to the polishing influent a digested wastewater that had a BOD of less that 10 ppm 95% percent of the time and less than 5 ppm for 67% percent of the time, barring mistreatment by the occupants.

    Preliminary treatment

    The septic tank serves as a trash tank to retain oil, grease, grit and large objects which may otherwise clog downstream piping and equipment.

    Primary treatment

    The septic tank also provides primary biological and physical treatment. Organic and inorganic solids settle out and remove some organic nitrogen, organic phosphorous and heavy metals. The main function of the septic tank is to ferment and biodegrade large organic molecules into smaller dissolved organics which are more readily degradable in the aerobic Biofilter. The septic tank further provides anaerobic digestion of the settled sludge and waste sludges from other subsequent treatment processes. In this case the septic tank effluent serves as an organic matter source for de nitrification of the Biofilter effluent.

    Secondary treatment

    The Waterloo Biofilter™ with air ventilation provides secondary treatment. It is an aerobic biological process which removes organic matter and effects nitrification. Forced air ventilation is provided by the household HRV guaranteeing occupant attention should a breakdown occur.

    Nitrification is the term generally given to any wastewater treatment process that biologically converts ammonia nitrogen sequentially to nitrite nitrogen and nitrate nitrogen. It does not remove significant amounts of nitrogen from the effluent. It only converts it to another chemical form. Nitrification can be done in many suspended and attached growth treatment processes when they are designed to foster the growth of nitrifying bacteria as in the case of the Waterloo Biofilter™.

    De nitrification can be achieved using many alternative treatment processes. In biological de nitrification, nitrate nitrogen is used by a variety of heterotrophic bacteria as the terminal electron acceptor in the absence of dissolved oxygen. In the process the nitrate nitrogen is converted to nitrogen gas which escapes to the atmosphere. A carbonaceous food source is required by the bacteria in these processes.

    For the Toronto Healthy Houses, de nitrification will be achieved in the recirculation tank by recirculating the nitrified Waterloo Biofilter™ effluent. The tank is downstream from the septic tank and therefore has the required carbonaceous food source for the denitrifying bacteria and an anoxic environment. It contains a wet well for the Waterloo Biofilter feed pump.

    The Waterloo filter, is very efficient in removing biological loading. As I understand it we can depend on it to remove 90 to 95% of BOD in a single pass usually. As we are planning to use it in a recirculating or multi pass mode removal will be much greater. However, it is my understanding that there will still be variation in the quality of the effluent from it.

    Safety

    One of the primary concerns I have with this system is ensuring that the system produces safe and aesthetic water reliably or none at all. While wastewater technology is dedicated to removing waste from water, drinking water technology is dedicated to ensuring that effluent is safe for consumption. For us the purpose of the polishing or reclamation stage is to ensure that the finished water is always acceptable no matter what the quality of the Biofilter effluent.

    As a layman becoming aquainted with on site wastewater treatment, I was surprised to learn that people who are expert in water filtration when it applies to preparing drinking water have very little contact with experts in water filtration as it applies to wastewater treatment. The combining of these two talents into one team, while not onerous, was refreshing and educational for me.

    Advanced Treatment - Polishing or reclaiming

    Following secondary treatment , advanced treatment and disinfection is provided based on the advice, designs, products and contributions by Bob LeCraw of RAL Engineering.

    Since I am not in possession of detailed or comprehensive understanding of drinking water filtration I am indebted to him since he agreed to share this presentation today.

    Presentation by Bob LeCraw

    WASTEWATER POLISHING TREATMENT

    The approach we have taken for the polishing steps of the wastewater treatment system is to use the multi-barrier approach of drinking water treatment technology. Our objective is to produce a reclaimed water effluent quality that is completely safe, beyond doubt, for direct human contact.

    The polishing treatment system is the identical process used for the potable water treatment and consists of a multi-media filter and ultraviolet disinfection. The filter is a unique adaptation of the slow sand filtration process. Traditional slow sand filters are very efficient at removing turbidity, bacteria and cysts but have been limited to very good quality influent water that is low in suspended solids and low in colour. In 1993 RAL Engineering Ltd. started development of a multi stage filtration unit for small communities that incorporates a roughing filter, slow sand filter, and activated carbon contactor. Pilot testing of this process and a subsequent full scale plant, have shown it to be a very effective method of water treatment that does not rely on the use of chemicals. The filters designed for the Healthy House potable and recycle water system are an adaptation of this concept.

    The roughing filter is a series of gravel layers graded from course at the bottom to fine at the top. This 'prefilter' removes a large percentage of suspended solids by filtration throughout the depth of the bed. It substantially reduces the solids loading on the slow sand filter and allows it to be used on water supplies that are much higher in turbidity than would be normally possible. The slow sand filter is a fine sand bed that develops a thin biologically active layer at the sand surface called the schmutzdecke. This layer becomes very effective in adsorbing particulates, bacteria and cysts and will consume a significant percentage of dissolved organic matter. Effluent from the slow sand filter is very low in turbidity and bacteria, and virtually free of cysts. Finally the water passes through an activated carbon contactor to adsorb colour, taste and odour compounds.

    The unique aspect of the Healthy House filter is that all three elements have been incorporated into a single tank. The filter is cleaned by back flushing about once a month and the carbon will be replaced about once per year. If the filter is not cleaned, when required, it will simply become plugged-up and gradually produce less and less effluent. Quality is not affected. If the carbon is not replaced only the aesthetic quality will be affected and serve as a reminder to the occupants that attention is required.

    As the final barrier to pathogens the effluent from the filters is passed through an ultraviolet disinfection unit. Treated water discharges to a 1200 L storage tank and is re-pumped into the reclaimed water system. By using a pair of check valves the stored water is forced to pass through the UV unit again as a further safeguard against bacterial re-growth in the storage tank. The ultraviolet unit is equipped with a UV sensor which will automatically shut down the supply if there is insufficient disinfection due to a burnt-out or fouled lamp.

    Both the potable and wastewater treatment systems uses municipal treatment technology in an innovative configuration to facilitate installation and operation. A failure to operate the system correctly will produce a reminder to the residents through reduced flow or poorer aesthetic quality without creating a health risk.

    A schematic of the treatment system for the Healthy House project is as follows;

     

    Involving the household in water treatment

    (Continuation of presentation by Rolf Paloheimo)
    Conventional wastewater treatment is a black box, or more appropriately a black hole to most consumers. They do not know or likely care what happens to their wastewater after they flush the toilet. If they are on a septic system, it is likely they will pay very little attention to it unless it backs up or fouls their drinking water. If they are on municipal services the only time they are concerned is when they pay their taxes or if beaches are closed as in Toronto after a summer rainstorm.

    This ignorance, of course is not the case for a system that reuses wastewater. By definition reclaimed wastewater is the same as water supplied to those fixtures that receive reclaimed water. If the treatment system breaks down it affects the water that goes to those fixtures. Our system includes multiple safeguards as you have heard from Bob LeCraw. Those safeguards actually cut off supply of water to fixtures in the house preventing the further generation of wastewater to a large degree.

    In addition to such safeguards, the residents will naturally monitor water quality as part of their everyday activities. Every time you look into the toilet bowl you are performing a crude turbidity test. Every time you enter the bathroom, you will do a crude odor test. Reclaimed water to the shower and bath provides even more intimate contact with the water ensuring user interest and awareness of the quality of treatment systems. The residents using the house will necessarily be more involved in ensuring high quality treatment since such tests naturally occur many times a day in most households.

    This "soft" monitoring and involvement with treated water, along with professional maintenance and periodic water testing, provides a powerful argument for allowing such systems as an alternative to septic and Class 6 systems or even municipal servicing in some cases. There are however some considerable regulatory barriers that make the approval of them possible only on a demonstration or "innovative approvals" basis at this time.

    Regulatory issues

    Water quality objectives

    As you have seen we have gone to considerable lengths to ensure high quality water is available from our system, however, what defines "high quality" in this case? Applying drinking water objectives doesn't make much sense since not all of the parameters are meaningful for the uses proposed.

    In the Toronto Healthy Houses it is proposed to use reclaimed wastewater for non-potable uses including; toilet flushing, bathing, showering, clothes washing and landscape watering. Other than swimming and bathing criteria for natural waters and swimming pools, there are no Canadian guidelines for these proposed reclaimed water uses. For guidance on establishing recommended acceptance criteria for the reclaimed water it is necessary to review water reuse practices in the USA.

    I am indebted to Mr. Al Townshend, P. Eng. of Blue Heron Environmental Technology for the research on water reuse standards.

    Ontario Swimming and Bathing Water Use Criteria

    ("Water Management" MOEE, Toronto, Ontario, November 1978)

    Water used for swimming and bathing should be aesthetically pleasing, devoid of any substance which would produce objectionable colour, odour, taste or turbidity. Because both alkaline and acid waters may cause eye irritation, the pH should be within the range of 6.5 and 8.5.

    The use of the water should not cause diseases or infection in the gastro intestinal tract, the eye, ear, nose or throat or in the skin. Such diseases or infections could be caused by pathogens including bacteria, fungi, protozoa, helminths (worms), or viruses.

    Bathing limits for recognized pathogen parameters are ;

    ParametersLimit per 100ml.
    Fecal Coliform100
    Total Coliforms1000 geometric mean density

    However, coliform bacteria determinations by themselves do not adequately predict the presence or concentration of pathogens, viruses, protozoa and helminths.

    US Water Reuse Guidelines

    This section considers the US Water Reuse Guidelines with respect to Water Quality parameters.

    The September 1992 USEPA Manual "Guidelines for Water Reuse" summarizes the criteria set for reclaimed water treatment and/or minimum treatment by those states which have water reuse regulations or guidelines. Generally, where unrestricted pubic exposure is likely in the reuse application, the wastewater must be treated to the highest degree.

    The most common parameters for which water quality limits are imposed are biochemical oxygen demand (BOD), the total suspended solids (TSS), and total fecal coliforms. The coliform indicators are used as indicators of disinfection effectiveness. A limit on turbidity is also usually specified to monitor process treatment performance.

    The USEPA review of existing state regulations for unrestricted urban use show a wide variation in requirements. Where specified the following ranges in limits are in effect.

    ParameterConcentrationComments
    BOD5 to 30 mg/LTexas requires the monthly average not to exceed 5 mg/L
    TSS5 to 30 mg/LFlorida requires a limit of 5 mg/L before disinfection in all samples
    Average fecal and total coliform limitsnon detectable to 200/100mlFlorida requires that 75% of the fecal coliform samples taken over a 30 day period be below detectable levels with no single sample in excess of 25/100ml

    Utah requires that no single sample exceed a total coliform count of 3/100 ml.

    At this time (1992), Arizona and Hawaii were the only states that have set limits on certain pathogenic organisms for unrestricted urban reuse.

    In Arizona, the pathogens include enteric viruses and Ascaris lumbricoides (roundworm) eggs. Arizona's allowable limit for the enteric virus is 125 plaque forming units (pfu) 40 L and none detectable for Ascaris lumbricoides.

    In Hawaii, the pathogens are enteric viruses and the allowable limit is less than 1 pfu/40 L.

    South Carolina requires that viruses be monitored but does not specify the type of viruses to be monitored or any limits.

    Turbidity2 to 5 NTUOregon requires that the turbidity not exceed 2 NTU (24 hour mean).

    California requires not more than 2 NTU.

    InorganicsResidential use of water typically adds about 300 mg/l of dissolved inorganic solids. Existing wastewater treatment technology generally can reduce many trace elements to below recommended levels for drinking water.
    OrganicsThe Organic makeup of residential wastewater besides naturally occurring humic substances and fecal matter includes food wastes, liquid detergents, oils, grease, cleansers and other discarded substances. Some of the adverse effects associated with these organic substances include;

    Aesthetically displeasing, they may be malodourous and impart colour to the water.

    Clogging, particulate matter may clog sprinkler heads or accumulate in soil and affect permeability.

    Disinfection effects, organic matter can interfere with chlorine, ozone, and ultraviolet disinfection, thereby making them less available for disinfection purposes.

    Health effects; ingestion of water containing certain organic compounds may result in acute or chronic health effects.

    The project team and CMHC are interested in involving the Province through the Ministry of Environment and Energy in developing and formalizing water quality objectives for wastewater reuse after the project is built and some data is available.

    Disposal regulation

    As we have seen a significant incentive for reusing water is to reduce the size of the disposal area. Unless regulations allow reduced disposal area where such systems exist there will be no reason to build them in Ontario.

    The need to dispose of smaller quantities and the ease with which highly treated water can be disposed of as compared to septic tank effluent or conventional Class 6 systems makes a convincing argument for allowing such a reduction.

    Allowing lower disposal areas for higher quality effluent.

    The regulation in Ontario calculates that septic tank effluent must be disposed of in a trenches where the length of the distribution pipe in metres in an absorption trench field is Q*T/200 with Q equaling quantity (1600 litres for a three bedroom home when reuse is not part of the system) and T is the permeability of the soil in minutes per centimeters. If the effluent has been improved by a "proprietary aerobic treatment system" , also referred to as a "Class 6" system, the calculation is improved to Q*T/300 resulting in a 1/3 reduction in area.

    If a sand filter is constructed as part of the disposal system the calculation is improved to a straight area calculation where the area in square metres is Q*T/850. The Waterloo Biofilter (in a single pass configuration) produces effluent roughly equivalent to sand filter effluent. It is reasonable that the criteria for sand filter leaching beds be applied to it and the approved ratio applied to it.

    Lowering the amount of water in calculations.

    Roughly 50% of water used in the average water in a typical household is used to flush toilets, adding laundry and bathing brings the total to 80%. The regulation in Ontario calls for a quantity of 1600 litres per day as the disposal amount for a three bedroom house. Reusing water 80% of the time cuts the need for disposal to 320 litres, without factoring in conservation, a very sizable difference. It is reasonable that such reuse be allowed to reduce the Q in the equation, provided that verification of plumbing arrangements be available.

    Future iterations of the design

    The wastewater systems in the Toronto Healthy Houses are prototypes, so room has been allowed to adjust flows, rearrange plumbing and otherwise tinker with the design in order to learn more about how they will work and to provide for backups if something goes wrong.

    In future is it easy to envision the processes used in the Healthy House wastewater system constructed in a single device or appliance, somewhat larger than a septic tank, with a disposal field underneath it. The beauty of it for a builder would be that installing and connecting it would be no more troublesome than installing a precast sewage tank or cistern. Difficult sites would be much easier to service.

    Cost

    The systems as built in the Toronto Healthy House project cost in the region of fifteen thousand dollars per unit. If the single wastewater appliance approach proves feasible then I estimate the cost to drop to about ten thousand per unit. If they can be manufactured in quantities over a thousand per year I estimate the cost would drop to $7500 per unit. That is competitive, in fact cheaper than servicing new subdivisions in many cases. It is also roughly comparable to a conventional septic system on a flat site.

    The cost of the systems in the Toronto Healthy House project has been partially subsidized by the participation of the suppliers as sponsors. The sponsors of the water systems in addition to CMHC include Wilkinson Heavy Precast who sponsored tanks in part, RAL Engineering, Trojan Technologies Inc., and Waterloo Biofilter.

    Marketing Issues

    Marketing is of course much more important than engineering to a businessman. Whether something works or is feasible is not important if no one will buy it. Here lies the greatest risk to the project.

    I can not report or predict whether wastewater reuse will be marketable. It seems there is a considerable amount of interest, however whether any of those people who are interested will actually pay money for such systems I do not yet know. For any new technology to gain acceptance it needs what marketing people call the "early adopters," those people who will adopt the latest and make it fashionable or hip. Then the rest of us catch up. Whether anyone can make wastewater reuse fashionable remains to be seen.

    On the other hand, governments are currently in a greater and greater cash crunch, they are therefore less and less able to subsidize new infrastructure. Regulators are more unwilling to approve septic systems than they have ever been. So there is greater and greater opportunity for alternatives to conventional systems in Ontario.

    In other jurisdictions, where the problem is a shortage of water, the case for such systems has a different underpinning. We have had inquiries from the middle east and from the Caribbean with respect to the system. Whether these are real opportunities, I do not yet know.

    Source : 

    http://mha-net.org/msb/html/papers-n/palo01/wastewa.htm

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