Abstract:
Conventional technology for wastewater treatment suffers from many disadvantages like high cost of erection, running and huge consumption of power. In many instances especially in developing countries in the tropical parts of the world, it is possible to successfully use aquatic weeds based waste treatment plants. Both floating plants based (like water hyacinth or Lemnids) and emergent plants (The Root Zone Technology) based systems have been found to be successful in treating a large variety of wastewaters. In the present study a water hyacinth based system was erected to treat 10,000 liters per day effluents from a light engineering industry and was monitored for one year. The performance of the system with regard to reduction in various waste constituents is reported here. The Engineering Industry (S.P.Engineering, Karad, India) produces housing shells for compressors and releases about 10,000 liters of effluent per day from various operations like polishing, degreasing, washing etc. The wastewater had high oil and grease content and was acidic in nature.
The hyacinth based system had an oil and grease trap followed by three interconnected tanks of 8.0x2.5x1.0 m water depth. The inlet was through a baffle 30 cm below the water level. The total area under the treatment was 60 m2. BOD loading was 156 kg.ha.day-1. A retention time of 6 days was provided. The average hyacinth cover maintained on the plant was about 75%. The range of inlet wastewater characteristics was: pH 5.98 to 7.64; conductivity 449-2062 µS/cm; BOD 43.0 to 98.0 mg/L; COD 88.0 to 266.6 mg/L; total Kjeldahl nitrogen 17.64 to
30.80 mg/L; inorganic phosphorus 1.1 to 7.36 mg/L; oil and grease 87.13 to 312.13 mg/L. The range of percent reduction in various parameters was COD 1.06 to 87.67%; BOD 33.33 to
78.67%; TSS 50.78 to 90.55%; TDS 9.29 to 38.82%; calcium 19.95 to 75.66%; magnesium
19.95 to 75.66%; sulphides 9.90 to 100%; sulphates 30.77 to 100%; total nitrogen from 14.81 to 89.19%; total phosphorus from 9.87 to 54.18%. The hyacinth harvested from the treatment plant was also periodically analyzed for nutrient content. Both calcium and magnesium content were higher in shoot as compared to roots and varied respectively from 0.541 to 1.80% and 0.717 to 3.67%. The phosphorus content varied from 0.512 to 0.982% and was higher in roots. The total nitrogen content of the plants varied from 0.71 to 4.28%.
