Gray Water System
Domestic water usage continues to put higher demands on municipal supplies and bigger costs on consumers. Only a very small fraction of daily water consumption is used for drinking and cooking. Gray water recycling for use as toilet flushing, irrigation and wash water makes economic sense. In arid regions where potable water is created at great expense by desalination, the economics are more attractive still. Gray water is usually considered to be all the waste water from a residence but excluding the black toilet water. Ideally suited to new build developments where dual drainage can be designed in at an early stage. The gray water is collected and treated separately from the black water. Retro fitting existing residential developments with dual drainage is more complex and the economics will need to be analyzed. The use of treated and recycled gray water within a development will also require a separate pressure supply from the potable water supply. This is already commonly used in some Far East nations.
Collection, Composition & Treatment of Gray Water
Gray water must be collected from a building in a separate drainage system from the black water. It may sound complicated but it has been common practice on commercial ships for decades. The gray water will be taken to a Gray Water Treatment Plant, either communal to serve a housing development or in the basement service area of an apartment tower. Gray water is essentially made up of shower & bath wash water, soaps, laundry water and other drainage water but excluding toilet water. It may or may not include kitchen water and kitchens are often equipped with garbage grinders. The water analysis will include solids both settle able and suspended, a moderate level of BOD and FOG (fats, oils and greases) both in a free form and emulsified from kitchen and shower/bath water. Kitchen waste water adds considerably to the organic load and will demand additional treatment equipment. The treated gray water to be recycled must have very low levels of BOD, FOG and suspended solids. Further, there should be no visible tints and the water shall be odour free and it shall be disinfected.
Treatment of gray water must address all of the contaminants and it must be treated to a quality whereby it is of use in daily life. Gray water treatment is often dismissed as a simple process requiring only a few filters and chlorination, however, this is far from the truth and these process are often abandoned due to process problems and smell. The reality is that gray water contains, solids, hair, organic contaminants, oils, bacteria and measurable levels BOD. Without addressing these pollutants in a proper manner, the water for re-use will not be of an acceptable quality.
Some of the individual process equipment required are as follows:
EFLO SEP. Settleable Solids can be easily removed by gravitational lamella settlers combined a with screen, free separator, a modified EFLO SEP. If kitchen water is excluded, then it may be possible to omit this stage. Oil EFLO EC. Electro Coagulation to remove colloidal particles, break out oily water emulsions, reduced BOD , remove tints, disinfect and produced settleable and floating flocked sludge. No chemical dosing required. Clarification Tank. To remove sinking and floating sludge. Media Filtration. To remove suspended flocked particles. Disinfection. Sodium hypochlorite dosing will disinfect and provide residual disinfection in the delivery side of recycled gray water back to the residents. Depending on the population served, this equipment can be skid mounted on a single skid or as multiple skids connected on site.