The average availability of water is reducing steadily with the growing population and it is estimated that by 2020, India will become a water stressed nation. Hence use of non-conventional sources of water is inevitable to meet the future challenges of scarce water resource in terms of sustainability, food security, income security and environmental safety.
The rapid expansion of cities and domestic water supply, quantity of grey/wastewater is increasing in the same proportion. As per CPHEEO estimates about 70-80 per cent of total water supplied for domestic use gets generated as wastewater. The per capita wastewater generation by the class-I cities and class-II towns representing 72 per cent of urban population in India, has been estimated to be around 98 Liters per Capita Per Day (LCPD) while that from the National Capital Territory Delhi alone (discharging 3,663 MLD of wastewater, 61 per cent of which is treated) is over 220 LPCD (CPCB, 1999). As per CPCB estimate, the total wastewater generation from Class I cities (498) and Class II (410) towns in the country is around 35,558 and 2,696 MLD, respectively. An overall analysis of water resources indicate that in coming years, there will be a twin edged problem to deal with reduced fresh water availability and increased wastewater generation due to increased population and industrialization.
Farmers in peri-urban areas use untreated sewage water for crop production. The adverse effects of untreated sewage water have been overlooked. Hence there is a need to create awareness among users and to compare the same with treated waste water in crop production. Even the 12th five year plan document says that economic growth of 8 to 9 per cent is only possible if water requirements of the expanding population can be met. Thus the present investigation on use of treated wastewater in crop production would improve crop productivity by reducing direct contamination with food crops.
Under Water4Crops Project, University of Agricultural Sciences, Dharwad, has identified the following experimental sites – Ugar Khurd (Distillery), University campus and Dharwad (Mavanur, Katnur and Gabbur), where wastewater has been in continuous use for several years. Wastewater and soil samples were collected and analysed for different physical, chemical and biological properties .
The pH of sewage water was slightly alkaline and remained largely unaffected over time and was slightly saline. The sewage water of UAS, Dharwad recorded slightly higher salinity (Table. 1) over the sewage water collected at three villages near Hubli. Total solids were relatively higher at Gabbur and lower at Katnur. But, irrespective of location, total solids were higher during July-August possibly due to mixing of sewage water with rain water. Same trend was observed with respect to total suspended solids. Total dissolved solids did not show such trend. High levels of phosphates were observed, irrespective of place and time of sampling . Total N in sewage water increased during summer and decreased during rainy season (July and August months) may be due to dilution effect.
Besides, higher bacterial populations were observed in the month of August and September in all the four locations. Thus during rainy season due to low salinity level, the waste water may be judiciously used with proper treatment.
The electrical conductivity of soils was slightly higher in soils sampled close to the stream (50 m) at Gabbur than those sampled away at all depths. Despite long term irrigation with sewage water, the EC build up was not appreciable at all three depths in all villages. At all the three villages they remained relatively lower in the surface and increased with soil depth. The EC remained nearly uniform in majority of the cases except for a slight increase at the surface layer in sites closer to the stream at Gabbur. This indicates that extensive use of sewage water can be safely practiced in crop production.
Industrial waste water:
Continuous application of spentwash for varied periods at large had no effect on soil pH at various depths. However, increased frequency of application of spentwash resulted in relatively lower pH values, the lowest pH (7.87) being recorded under continuous application of spentwash for > 20 years. Application of spentwash for 15 to 20 years showed no significant effect on soil salinity. However, application of spentwash for more than 20 years resulted in accumulation of salt. The salt accumulation was more at the surface and decreased with depth. (plate. 1)
Continuous application of spentwash resulted in higher organic carbon status in soils. The organic carbon was low in the untreated control which increased to 4.78 g/kg due to continuous application of spentwash for 5-10 years, which further increased to 6.40, 7.20 and 7.74 g kg-1 due to continuous application of spent for 10-15 years, 15-20 years and > 20 years, respectively. Hence the trails were initiated at Ugar khurd to find out suitable agronomic and bioculture practices to improve soil fertility and productivity of affected soils.