All households irrespective of their economic strata generate grey water. Grey water pollutes common water bodies, underground water resources and becomes the source of many health problems. The people mainly affected however belong to those who live in the bottom of the economic pyramid.
When all Grey water collected from households get discharged into a common water body, it can gradually kill the water body. Most of the Municipal and Rural Grey water usually get discharged into water bodies in an untreated way. These result in (i) Diseases, (ii) Loss of natural resources and (iii) Pollution etc.
Need for Grey Water Treatment
• Recycling of water is considered a healthy ecological practice.
• However, when grey water is recycled without treating properly it leads to accumulation of heavy metals.
• It pollutes both the soil as well as underwater resources.
• There is not much awareness regarding this serious issue.
Analysis of Grey Water (general figures and will vary from place to place)
pH : 9.63
Conductivity : 0.170 S/m
Dissolved Oxygen : 8.14 mg/l
Salinity : 0.1 %
Total Dissolved Solids : 1.1 g/l
Oxidation Reduction Potential : 82 mV
Fluoride Concentration : 0.216 g/l
Potassium Concentration : 2.18 mg/l
Ammonia Concentration : 1.80 g/l
Chloride Concentration : 2.58 g/l
Nitrate Concentration : 1.56 mg/l
Calcium Concentration : 3.54 g/l
A Holistic Solution
• Grey water can be treated by the combination of mechanical, physical, chemical and biological methods.
• Cost-effective grey water treatment structures
• Biological agents like plants that remove heavy metals and other nutrients
• Combining these to have optimum treatment of the grey water
Methods to treat Grey water components
• Particulate matter removed by Soak Pit
• Colloidal particles by precipitation
• Dissolved material by phytoremediation
Soak pit – Settling pit
• Soak pit is a concrete structure.
• The size depends on total quantity of grey water to be treated and the amount of particulate matter in the grey water.
• Normally the size of soak pit ranges 1/25 to 1/30 of the available grey water.
• Eg. For 1000 lit. grey water the soak pit size should be of a capacity of 300 lit.
• The Grey water has to be retained 5 - 8 hrs. in the soak pit so that the particulate matters settle down on the bottom which can be removed periodically.
• The water coming out of the soak pit will be almost free from particulate matters
Removal of heavy metals
Heavy metals if any in the grey water, like cadmium, nickel, selenium, lead etc. have to be removed by proper adsorption and absorption agents –like non-edible plants and inert materials-before letting the grey water in to the soil for phyto remediation. After removal of toxic substances, the detoxified grey water can be used for irrigation.
Removal of heavy Colloids
• Colloids are molecular aggregates which are suspended in grey water.
• will not normally settle down and will be carried by the grey water.
• will not allow sun light to pass through and the water will have a very high BOD.
• will not support algal growth
• injurious to micro flora, plants and the soil.
• continuous accumulation will make the water bodies biologically dead and will also lead to swamp formation and eutrophication.
• creates foul smell and breeds worms
• can be precipitated out with the help of natural compounds like lime, gypsum etc.
Phytoremediation
• The dissolved nutrients like nitrates, phosphates and other compounds like that of Mg, Zn, K, Na etc. can be easily removed by plants and will be utilized for their growth and development.
• Passing the grey water through a canal on the sides of which are planted specific plants like Canna indica, Wild Taro, Typa angusta, Reeds, Napier grass, and Bamboo will suck all the nutrients and the water left out will be almost clean.
• When the water passes through tuft root system of plants, along with the absorption of nutrients the oxygenation of water also takes place increasing BOC and decreasing BOD
From Source to Grey water treatment system: a live model
Conclusions
India is now facing a severe water crisis. This is due to the large population and increase in the consumption. Grey water recharging offers a second alternative to improve the ground water. However, this should be done with caution so that it does not pollute the ground water. The advantage here is that this source of water is available on a daily basis in each household.
Reducing treatment requirements:
• This can be done by minimizing the use of cleaning chemicals such as colored toilet dyes. Natural cleaning products should be used wherever possible.
• Using a sink strainer to help prevent food scraps and other solid material from entering the waste water which will reduce maintenance cost.