Irrigation management using small scale filter for safe use of municipal wastewater

Abstract

The share of fresh water towards irrigation is predicted to be declining from 84.7 percent to 74.1 percent by 2050 whereas the expected demand for irrigation will hike up to 1072 BCM. At present about 65 million hectare, or 45 per cent of about 141 m ha of net sown area of the country is covered under irrigation. Government has taken initiative to provide water to every farm with the motto of har khet ko pani for increased production and better livelihood. One of the challenges to meet the target is to explore the feasibility of use of treated municipal wastewater for irrigation in peri-urban areas. As per CPCB 2015 assessment a total of 61,754 MLD of wastewater is generated out of which only 18,883.2 MLD is treated and rest are discharged in the water bodies deteriorating the quality of water and polluting the fresh water resources. Wastewater irrigation along peri-urban areas is becoming popular day by day owing to its rich nutritional status and nearby availability. But the heavy metal content and the microbial load in the wastewater poses threat to the growers as well as to the consumers. Treating the entire quantity of wastewater generated in Class I and Class II cities centrally is not feasible as it requires huge infrastructure and land areas. An attempt has been made to treat the wastewater at the receiving end through development of a small scale filter for its safe use in irrigation in peri-urban areas. A four chambered filter has been developed using suitable laboratory tested coarser and finer materials to reduce turbidity, BOD and heavy metals viz., Cd, Cr, Pb, Ni from the wastewater and its hydraulic behavior and filtration efficiency was evaluated. When tested through an open flow not as a pipe flow to take care of the resistance of the component of the filter with a head of 0.5 m the discharge was 1 litre per minute with 100 per cent efficiency to remove sediment and Cd. Further, the filter was modified by increasing the finer particle size and the discharge was increased with 1 HP pump and the output flow recorded was 0.5 litre per second with 50 per cent flow efficiency. With increasing the discharge rate to 0.5 l/s the efficiency of filter in reducing the sediment and cadmium content was 60 and 82.5 per cent respectively. This is due to the reduction in opportunity time while passing through the filter. The filter was further modified and redesigned by increasing the size of the compartment containing the finer particles from 3" to 5". The filter was evaluated in the farmers’ field through drip irrigation system and it has been observed that the average discharge varied from 1.38 to 1.43 lph with an average uniformity coefficient of 98.1 percent.