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Rolf Paloheimo

How does the Healthy House System work?

The general approach in the Healthy House Water System is to utilize highly efficient and passive wastewater systems able to biologically digest organic. This is followed by a polishing stage, where both passive and active methods are employed to assure a high quality, safe, and aesthetically pleasing finished water

In the Healthy House Water System all wastewater, grey and black, is combined and treated together.

Any facility can be viewed as a system where the disposal of wastewater must necessarily equal the amount of potable, or fresh water, brought into it, less irrigation and evaporation. The less fresh water used or available the more recycled water must be re-circulated in a facility. For instance on average only 200 L of fresh water was estimated be available to the Toronto Healthy House yet the typical water usage for the family of four living in the house is 1,000 to 1,200 L/day even with water efficient appliances. This means, in the Toronto Healthy House, water must be reused up to five times before being ultimately discharged. This is a very important consideration in the design of the treatment process as certain dissolved solids in the wastewater will tend to accumulate.

The Healthy House wastewater reclamation system consists of preliminary, primary, secondary, and tertiary treatment plus disinfection. The wastewater treatment systems used are suitable for domestic wastewater up to approximately 400 mg BOD5 (5 day Biological Oxygen demand) per litre of wastewater.

Treatment Criteria

For small systems, preliminary, primary and secondary treatment results in;

BOD5 of less that 10 mg/L 95% percent of the time BOD5 of less than 5 mg/L for 67% percent of the time Suspended Solids (SS)m less than 10 mg/L

Tertiary treatment results in;

BOD5 of less that 5 mg/L Suspended Solids (SS)m less than 2 mg/L Turbidity less than 1 ntu, typically 0.5 NTU Total coliform less than 2 per 100 mL Free of colour and odour

Preliminary treatment



A Septic tank sized for three days retention time 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 (secondary treatment). The septic tank acts as a mesophilic digester providing anaerobic digestion of the settled sludge and waste sludges from other subsequent treatment processes. In this case the septic tank also serves as a carbon source for denitrification of the Biofilter effluent.

The second stage of the primary treatment provides anaerobic filtration and digestion of colloidal solids. The process is proprietary to CCRI and was developed with the assistance of Mr. Al Townshend, P.Eng. and Dr. Jacek Mlynarek of SaGeos in Montreal. It consists of a cloth filter on which a slime develops to contact and digest solids coming in contact with it. The filter is passive, will not clog and does not require renewal or servicing under normal conditions. Because organic solids are converted to soluble gases, liquid carbonaceous food and water, sludge production is almost eliminated. Sludge production is limited to non biological elements (such as sand or other grit) present in the wastewater.

Secondary treatment




The Waterloo Biofilter developed by Dr. Craig Jowett, P.Eng., provides secondary treatment. It is an aerobic biological process which removes organic matter and effects nitrification. Nitrification is the process that biologically converts ammonia nitrogen sequentially to nitrite and nitrate nitrogen. It does not remove significant amounts of nitrogen from the effluent but rather converts it to a more stable form. Nitrification can be achieved 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.

Biological denitrification is also achieved in which 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 Healthy House System, denitrification is achieved in the septic tank by recirculating the nitrified Waterloo Biofilter effluent. The tank has the required carbonaceous food source for the denitrifying bacteria and an anoxic environment. The Waterloo filter, is very efficient in removing biological loading. It can remove 90 to 95% of Biological Oxygen Demand in a single pass and much greater removal in a recirculating or multi pass mode removal.

Tertiary Treatment

The approach used for tertiary treatment process draws on the multi-barrier approach of drinking water treatment technology. The objective is to produce a reclaimed water effluent quality that is completely safe, beyond doubt, for direct human contact.

This polishing treatment system is a process developed for potable water treatment and consists of two stage biological filtration with pre-ozonation and ozone 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 subsequent full scale plants 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 water system are an adaptation of this concept.

The roughing filter consists of graded, gravel and course sand. This pre-filter 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.

After the roughing filter the water passes through an ozone pre-contactor. The ozone pre-contactor uses excess ozone from downstream disinfection to contact the water prior to final filtration. The addition of ozone oxidizes some elements that would not otherwise be removed by the biological or physical treatment processes. Aerobic bacteria work by absorbing nutrients through their cell walls, large molecules such as lignins or tannins are difficult for them to digest. Ozone oxidation cuts up those larger molecules rendering them more easily digestible. Ozone is delivered along with oxygen raising the oxygen concentration in the water. The combination of these effects improves the operation of the slow sand filtration.

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.

The unique aspect of the smaller Healthy House filters are that they can be backwashed automatically whereas conventional slow sand filters are normally scraped manually. Slow sand filters contain passive guarantees of efficiency. If filters are not cleaned, or are overloaded, they simply become plugged-up and gradually produce less and less effluent. Quality is not affected.

Disinfection

As the final barrier to pathogens the effluent from the filters is ozonated. Treated water discharges to a storage tank and is pumped into the reclaimed water system. By using the water pump to recirculate water from the treated storage past a venturi ozone injector, the storage tank has ozonated water constantly recirculated to it.