Small Gray Water Recycle Treatment System

Over the years, awareness in environmental preservation has prompted the use of Gray Water Recycling System to treat and reuse back the recovered non-portable water as a source to flush toilets and urinals. Quite a number of small on-site self-contained facilities are developed and built on new commercial buildings and even in unsewered areas in remote locations with small communities, these are seen as a viable option for long term wastewater solution. Recycling also provides an option to deal with problems related to fresh clean water supply shortage.

gray water recycling systemTreatment of gray water which is termed as the wastewater coming from household fixtures and appliances except for toilet discharge, will often pose a challenge because sometimes presence of soap and laundry detergents that act as natural emulsifier to form emulsion with oils and fats will cause difficulty in processing steps. Normally in a small on-site system, there are 4 main treatment stages involved before the water can be reused back. First of all, septic tank is needed whereby the main constituents like solids and trash have to be removed. Next after the separation has taken place, the water is diverted to a biological treatment vessel so that aerobic breakdown of organic components can take place and degrade the material. Supply of sufficient air to create high dissolved oxygen condition is nevertheless the most important aspect here and the presence of aerobic bacteria has to be maintained in the right amount by periodically removing the waste sludge buildup. This is similar to a normal suspended growth biological treatment process.

After the gray water has undergone this crucial stage, it will be diverted to another separate processing unit whereby normally a self-cleaning ultrafiltration system is put in place to remove the carry over of bacteria and microorganisms from the biological step. Apart from that, the aim of setting up this unit is also to get rid of residual solids so that the water is free from all the contaminants. In the last and final stage, normally there is combined system comprising of an activated carbon vessel plus an ozone disinfection facility to polish and kill off the harmful microorganisms that might still be present so that the water is safe for reuse. Overall, the whole combined system is very cost demanding not only on the setup and construction stage but on the aspect of scheduled maintenance such as replacement of the activated carbon, the cost of generating air supply in compressors used in the biological treatment step and lastly on the waste sludge removal part and all these will be seen as the major obstacles to prevent its widespread application.

In places whereby there is an absence of treatment facilities, further complications will arise on how to handle the sludge generated in the small systems as discussed earlier. With these, come into mind several considerations on where we can dump the material and the need to search out a site suitable for disposal of the septic tank effluent. Usually soil testing is carried out to identify its characteristics, followed by percolation testing and this includes hydrogeological site evaluation as well, all have to be carried out so that a suitable location can be identified as disposal field. Design objectives has to be properly studied and mapped out because not only evaluation has to be done on the treatment performance of the gray water recycling system but also on whether the selection of disposal field will contribute towards contamination of groundwater quality. Primary constituents like nitrogen and phosphorus, bacteria and microbes all has to be measured on the effects of leftover and the impact it will cause to the environment. All in all, selection of design criteria for the development of a fully functional and effective on-site wastewater management program has to be carefully studied before being implemented. Related topic: Reuse of wastewater in agricultural and industrial application

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