Grey water treatment and reuse - CSIR - NEERI Technology

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Grey water treatment and reuse

Greywater is wastewater generated from domestic activities such as laundry, dishwashing, and bathing. Greywater is just washwater. There are many differences between greywater and toilet wastewater (called "blackwater").  These differences  tell us how these wastewaters should be treated /managed and why, in the interests of public health and environmental protection, they should not be mixed together.

Differences between Greywater and Blackwater.

  • Greywater contains far less nitrogen than blackwater
  • Greywater contains far fewer pathogens than blackwater
  • Greywater decomposes much faster than blackwater

Recently I visited CSIR technofest 2010 showcased by Council of Scientific & Industrial Research, New Delhi, at India International Trade Fair in New Delhi, the Capital of India.  In this technofest, I have seen a technology  "Grey Water Treatment and Reuse" which was developed by NEERI (National Environmental Engineering Research Institute), Nagpur, under the aegis of CSIR, New Delhi, India.

NEERI was involved in development of grey water treatment and reuse systems at institutional and household levels. The grey water reuse systems collect, treat and reuse bathroom water (shower, nontoilet / black water) for flushing of toilets. The drive for this technology was a result of decreasing availability of water and lowering of groundwater table. Grey water treatment plants constructed in the institutions, particularly in residential schools (Ashrams) in Madhya Pradesh, mainly consist of sedimentation or settling unit and filters. Process of sedimentation allows removal of suspended solids by gravity and natural aggregation of the particles without use of coagulants. The major processes in filtration are sedimentation in the pore spaces, adhesion to the media particles, and bio-chemical degradation of captured particles in slow-sand filter. The concept of grey water reuse from the institutions has been extended to the households to treat and recycle grey water. This system also consists of sedimentation and filtration, and possible reuse of treated grey water includes toilet flushing and irrigation. A design of grey water treatment system developed at household level.

In order to conserve water by recycling and reuse of grey water as an alternative source for toilet flushing and gardening / irrigation etc, a NEERI residential quarter was selected to study the detailed quantification, characterization and reuse of wastewater generated from bath, wash basin and laundry (excluding kitchen wastewater). Grey water treatment plant was designed and constructed for a flow of 480 lit/day.

Based on the daily observations, daily potable water demands for a household and grey water generation from bath, laundry and wash basins were observed to be 165 LPCD and 80 LPCD respectively. And for reuse for toilet flushing and irrigation of an area of 22 sq m the water demands calculated to be 24.50 LPCD and 46 LPCD respectively. The following diagram shows the grey water generation and reuse on per capita basis for a period of three weeks.

The study revealed that about 40% to 60% potable water can be saved by reuse of grey water. It is estimated that about Rs. 6 lakh ($13500) / year water charges can be saved if recycled grey water is used for gardening, irrigation and for toilet flushing in the households of NEERI Colony. Recycling and conservation of water in urban areas is therefore an essential contribution to the future environmental sustainability. The performance of grey water treatment plant based on the grey water quality was assessed. It is found that the BOD and COD were removed on an average 82% and 61 % respectively.  Grey water may be used for toilet flushing and irrigation or gardening.

The below links may be useful for more details and information.





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This article was published on 2010/12/11