Reclaimed Wastewater Quality Assessment for Irrigation and Its Mid-Time Reuse Effects on Paddy Growth and Yield under Farmer Management

Many studies have been conducted on irrigation of upland crops with reclaimed wastewater while there have been a few reports about wastewater reuse for paddies. The majority of irrigation water requirement of paddy field in Bandargaz region (Iran) during the dry season within the last 12 years is dependent on effluent of treatment plant. Accordingly, different water parameters and 12 irrigation water quality indexes and economical- environmental filed management factor (fertilizer application rate) and crop growth and yield were studied in freshwater (FW) and wastewater (WW) filelds.

Unexpectedly, wastewater and freshwater salinity was less and more than the threshold salinity of paddy (2.0 dS.m^-1), respectively and due to the high concentration of chlorine, FW is not suitable for irrigation. Based on almost all of indices and standards for assessing irrigation water quality, WW was significantly better than FW.

The average concentration of heavy metals in both FW and WW samples were in the order of Cr˂Cd˂Pb˂Ni. However, results showed that concentration of heavy metals in WW was significantly more than FW. Nevertheless, these were below maximum allowable based on international standards and guidelines. The average nitrogen concentration in the reclaimed wastewater was 11.2 mg.lit^-1 that was more than the required nitrogen concentration (7 mg.lit^-1). So, a dilution strategy could be adopted when reclaimed water is used. No significant difference was observed in two type farms based on plant height, spike length, and 1000-seed weight, but this factor was significantly effective on seed per spike and seed yield so that they were higher in WW irrigated farms by 12.4 and 10 percent, respectively.