Use of domestic wastewater and sewage effluent in irrigation of agricultural crops

Use of domestic or municipal wastewater for irrigation of agricultural plants is very important in arid and semi-arid areas, because of the shortage in water resources with suitable quality. These kinds of applications need the regional researches due to climate, soil, plants and cultural varieties. In order to study the soil-plant complex effects as a biological filter on reducing the wastewater pollutants and to investigate the transformation of them below the root zone as a result of irrigation, a series of lysimeter studies were carried out in Tehran area. A statistical “factorial experiments in the form of randomized complete designâ€‌ (3 أ— 3 أ— 3) was used. Raw and treated domestic wastewater of Ekbatan housing complex and well water (control) have been applied for irrigation of raw edible vegetables such as parsley, carrot and tomato for two years. The results showed a 99% - 100% BOD5 reduction which was measured in drainage water of lysimeters in both raw and treated wastewater. The COD rate of drainage water was low at the early stage of plantation and increased by continuing the irrigation up to maximum level, then reduced in the ending period of experiment. Mass balance analyses indexed by COD showed an efficient reduction of 93% to 99%. Nitrogen transformation through soil to drain depth, were between 12.93% to 33.75% of entranced amount for irrigation with raw wastewater and 23.30% to 38.17% for treated wastewater. This amounts for phosphorous were about 0.9% - 3.56% in raw wastewater and 1.03% - 4.15% for treated one. Maximum EC transformation to drain depth was observed in well water, treated and raw wastewater irrigated lysimeters respectively. Increasing the depth of sampling has increased EC. The behavior of pH in water samples was against the EC. The maximum production for tomato and carrot has been obtained by using the raw wastewater, but it was minimum for parsley. The amount of nutrients (N as protein, phosphorous and potassium) was maximum in all crops, in result of irrigation with raw wastewater, but the protein level was lower than normal amounts which are presented in standard tables for crops of Iran. P and K adsorption have been near or more than normal levels in all crops. Soil hydraulic conductivity increased by using wastewater for irrigation and applying the raw wastewater happened maximum rate. The most increase of organic matter in the soil was happened in result of irrigation with raw wastewater and carrot planting. After two years and completion of self-digestion period, raw and treated domestic wastewater caused 48.8% and 17.4% increase in soil organic matter content respectively, but reduction of 31.5% was found in control treatment compared with the original amount. Also, There was a direct relationship between the reduction rate of soil organic matter and the amount of exceeded organic matter by wastewater application.