Study On Treatment Of Bio-diesel Wastewater Using Aerated Adsorption Technology

Numbers of methods have been applied in oil-containing wastewater treatment and among them adsorption has been proved to be a fast and effective process. The main problem associated with the adsorption technology, however, is its high cost in regeneration of the system adsorption capacity. The present study was thus conducted to compare the efficiency of pollutant removal from wastewater generated from bio-diesel production among three designed treatment systems:aerobic adsorption, anaerobic adsorption and aerated-KMT (a bio-film technology). The main objective of the designed tests was to investigate the feasibility of regenerating the system adsorption capacity by means of aerobic digestion of the adsorbed organic pollutants. The results obtained from the repeated experiments are summarized as follows:(1) Activated carbon was found to have the highest adsorption capacity among the five tested adsorbents with respect to the removal of organic pollutants from bio-diesel wastewater, and its COD adsorption capacity was determined in the range 25-32 mg/g. Artificial zeolite was shown to be effective to remove TN and TP while hydrotalcite was effective to remove TP. Due to the release of large quantities of self-containing organic substances into the solution, the three tested organic adsorbents, bamboo scraps, grains and cotton seed hull did not reduce but instead increase the concentration of COD, TN and TP of the treated wastewater to extremely high levels, resulting in much worse water quality of the effluent.(2) The aerobic adsorption system using activated carbon as the adsorbent was shown to have high treatment efficiency in removal of organic pollutions from bio-diesel wastewater. At the end unit of the aerobic adsorption system, the total removal rate of COD amounted to 93～98% and the COD content of the effluent met the first grade B of the national stipulated discharge standard (GB 18918-2002); the removal rate of the grease reached 88～90% and the contents of total oil, plant oil and animal oil all met the second-grade of the discharge standard; both TN and TP in the effluent met the first grad A, and the effluent pH was maintained in the whole tested period within the allowed discharge range.(3) There were significant differences among the three designed processes (aerobic adsorption, anaerobic adsorption and aerated bio-film digestion) with respect to their removal efficiency of COD from the tested wastewater. The removal rates of organic pollutants of the tested systems followed the order:aerobic adsorption (Ⅰ)> anaerobic adsorption (Ⅱ)>aerated bio-film digestion (Ⅲ). The present results indicate that under the experimental conditions, either a single absorption or a single aerobic bio-digestion process cannot be directly applied to treat the wastewater generated from bio-diesel production.(4) The treatment efficiency of the aerobic adsorption system is related to the numbers of sequenced treatment cells. As the pollutant concentration in the tested wastewater was very high, treatment using a single treatment cell could not reduce the pollutant content of the effluent down to an allowed discharge point. In the combined sequenced treatment cells, the significant reduction of the pollutant concentration in the previous cell led to a greatly lowered pollutant load for the following cell, thus ensuring the water quality of the effluent at the end cell finally to reach the stipulated discharge standards.(5) In principle the designed aerobic adsorption system is equivalent to a combination of "aerobic+anaerobic+adsorption", which is similar to an "A2/O+adsorption" process. In the whole tested treatment period the contribution of aerobic bio-degradation in all sequenced adsorption cells was found between 30～45% and the total pollutant removal rate of the aerobic adsorption system was consistently maintained at high levels. The effect of the adsorption capacity regeneration in the tested aerobic adsorption system reached the designed goal that the sum of the contribution rate of aerobic bio-digestion equals the designed pollutant removal rate, thus maintaining the stability and sustainability of the treatment system at relatively high levels.The present study provided a new model as alternatives for treatment of oil-containing wastewaters. The results obtained from the tests are of both theoretical and practical values in development of technology for treatment of oil-containing wastewaters and protection of ecological environment.