Studies on the Rice Husk Ash Based Filters for the Treatment of Pulp and Paper Industry Wastewater

Abstract

The demographic growth, urbanization, industrial development and climate change have fundamentally changed water issues. Industrial wastewater constitutes major source of metals, toxic materials, chloride contents, alkalinity, acidity etc. It is thus necessary to invent new models and solution to meet the local needs of water users. Paper manufacturing is highly capital, energy and water intensive industry. The effluent from these industries contains high level of Total Dissolved Solids, pH, Biological Oxygen Demand, Chemical Oxygen Demand and Colored Organic Compounds. The treatment of pulp and paper wastewater has been carried out with activated sludge process, anaerobic digestion, aerated lagoons and biological filtration method which results in the reduction of BOD to permissible levels but Total Dissolved Solids (TDS) content persists. So there is a need for the reduction of TDS so that the treated wastewater can be used for irrigation purposes. The main agroresidue raw materials used in pulp and paper industries are wheat straw, baggasse, sarkanda grass, jute rags as well as waste papers. Rice production is an important part of our national economy. During milling of paddy about 78% of weight is received as rice, broken rice and bran and rest 22% of weight is received as husk. This husk is usually used in boilers for producing steam or electricity and after the firing process solid is mass left out which is termed as Rice Husk Ash (RHA). RHA is collected from the particulate collection equipment attached upstream to the stack of the rice husk fired boilers. In India about 20 million tonnes of RHA is produced annually. This RHA is great environment threat causing damage to the land and surrounding area in which it is dumped. So there is a need to find the alternative uses of RHA. One technique may be the preparation and application of RHA based filters in the treatment of industrial wastewater. RHA based Column and Ball filters with different composition of cement, RHA and sand were prepared for the reduction of TDS, TSS and chloride content from secondary treated wastewater sample. The effect of different parameters like contact time, size of the filters and treatment efficiency were evaluated. Obtained results indicate that ball filters are better than column filters and optimum composition of ball filter was found to be 100 g cement, 50 g sand and 50 g RHA for wastewater treatment. The results showed that 71% reduction in TSS, 51% reduction in TDS and 51% reduction in concentration of chlorides was obtained after 9 h of exposure time. The experiments to prove filter repeatability were also conducted which showed that the treatment efficiency was increased from 14 to 43% in column filters and 23 to 51% in ball filters after 5 days and thereafter, the efficiency decreased to 19 and 29% respectively after 10 repeated cycles. So, it is evident from the results that the RHA based ball filters can be employed efficiently for the treatment of wastewater at a tertiary stage for the reduction of TDS before its safe discharge. Thus, RHA based filtration can be applied in conjuction with the existing biological processes for the treatment of TDS removal in wastewater from agro residue based pulp and paper mill.