Preparation of filters for water and wastewater purification using rice husk ash

Abstract

The ground water supplies have become highly contaminated by the addition of undesirable substances that have rendered it unfit and toxic for various purposes, especially for drinking. The main ground water quality problems in India are due to salinity, arsenic, nitrates, fluorides, uranium, heavy metals, oils, etc whereas the discharge from industries is also polluting the water as it is high in salinity, heavy metals and other impurities. India is primarily an agriculture-based country and its economy largely depends on agriculture. It is one of the world's largest producers of white rice, accounting for 20 % of all world rice production. Rice milling industry generates a lot of rice husk during milling of paddy. During this process about 78 % of weight is received as rice, broken rice and bran. Rest 22 % of the weight of paddy is received as husk. This husk is used as fuel in the boilers to generate steam for heating and power generation. This husk is converted into ash during the firing process which is termed as rice husk ash (RHA). RHA is of great environmental concern because of its detrimental effects to the land and the surrounding area in which it is dumped. In order to combat the problem of water pollution and disposal of RHA, the use of RHA has been explored in making of filters which are used for the treatment of water/waste water. The RHA based ball and column filter were prepared using different composition of RHA, cement and sand. Drying and curing were important part of the preparation process. The method for optimization of contact time and composition was followed and the treatment efficiency was determined. The main focus was on the reduction of TSS, TDS, turbidity and concentration of chlorides and sulphate from water samples collected from various locations by using RHA based filters. The observations indicate that the ball filters were better in TDS and TSS removal than column filter. The optimum time for reduction of TDS from water samples was reported to be 4 h and the optimum composition of ball filter was found to be 100 g cement, 50 g sand and 50 g RHA for water and wastewater purification. The RHA based ball filter showed up to 88% reduction in TSS, up to 43 % TDS reduction and reduction in concentration of chloride up to 47% for waste water. The mild reduction in sulphate concentration was also reported. When the silica content was reported to be 11.3 mg/l from 11.1 mg/l after 6 h of treatment with RHA based ball filter in the ground water sample from Patiala. Upto 60% reduction in turbidity was observed in case of industrial sample which had high level of turbidity before treatment. An experiment to determine the repeatability and reusability of ball and column filter was conducted and it was observed that the ball filter showed about 10% efficient after 10 cycles of treatment whereas the efficiency of column filter came out to be 5% just after 4 cycles of treatment. So, the results conclude that the utilization of rice husk ash in the making of ball filters for the treatment of drinking water and industrial wastewater has been found to be efficient.