Effects of wastewater recycling from natural rubber smoked sheet production on economic crops in southern Thailand

Production of rubber smoked sheets of Thailand is carried out by over 700 small cooperative rubber sheet factories (CRSFs). A survey of CRSFs in southern Thailand revealed that most do not have adequate treatment for their wastewater. To investigate potential of this wastewater for agricultural use, a representative CRSF in southern Thailand was selected as a study site. Results showed that the waters in all the treatment ponds were in anaerobic state, and the final effluent from the system had never met the discharge standards. In the first experiment, pH of the final effluent was adjusted by the residual ash from fuel rubber wood, used in rubber smoking, before being mixed with tap water at ratios 1:0 (pure effluent), 1:1, 1:2, 1:4 and 0:1 (pure tap water as control). The experiment was carried out in a glasshouse where Chinese green mustard and cucumber were used as test plants. Results showed that the plants irrigated with effluent mixtures had higher yields than those plants in the control set, and the ratio of 1:2 with ash addition showed a prominent result.In the second set of experiments, impacts of effluent on economic crops, rice and rubber tree, were investigated. It was found that the latex production of rubber trees irrigated with effluent was significantly higher, at 112 ± 49% on average. However, in the paddy field experiment, empty-grain occurred in the effluent irrigated plot more than the control plot. This might be due to the impact of effluent application at grain-filling period. On the other hand, effluent application at pre-flowering significantly increased seed yield as compared to the applications at other stages of plant development and the control. Knowing the potential and method for correct application is of interest to the farmers since it can increase crop yields and reduce spending and application of chemical fertilizer, and finally eliminating additional cost for wastewater treatment.