The Performance Variation And Failure Factors Analysis Of Long Term Running Biological Activated Carbon

For the biological activated carbon(BAC) which is used as an advanced treatment process in water plant, the performance evaluation of activated carbon is the main basis for judgement of the time to replace or thermally regenerate of activated carbon. Considerable evaluation methods of new activated carbon were researched, while few study of evaluation about the long term running BAC had been carried out. In this paper experimental results of five continuous flow laboratory scale BAC columns filled with BAC of different operating time were discussed. The running time of the five BAC were 0 year, 1 year, 4 years, 8 years and 9 years respectively. The result showed variation of adsorption and biodegradation of BAC with running time. Later on, the failure risk on performance and running of the five BAC were analyzed and the failure factors were studied to guide the change of carbon.The research on function of BAC indicated that the five BAC had remaining adsorption capacity, but BAC could not play the role of adsorption due to the existence of desorption and biofilm in actual operation. The removal part of organic was mainly biodegradable dissolved organic carbon(BDOC). The pore size between 10 nm to 30 nm had significant relationship with biomass, and biomass had a significant impact on performance of BAC.The failure analysis on performance of BAC indicated that, the treatment effect could not be used as a failure indicator for the low organic concentration in water in Shenzhen area. The pore structure of BAC was thought to have significant relationship with performance of BAC filter. The pore volume with aperture between 10 nm to 30 nm could be used to indicate the performance variation of BAC. The long term running BAC had capacity to remove organics. The removal rates of BAC8 and BAC9 with operating time over 8 years were less than 20%, but the effluent could still meet the national standard of drinking water. The five BAC filters had ability to remove the trace quantity object pollutants phenol and odor compound 2-Methylisoborneol(2-MIB). But they could not ensure the effluent quality to meet the standard. Based on the adsorbate analysis, the BAC were found to have effective enrichment of metal, organic and inorganic. The adsorbates could cause water quality problem if they were released to water.The research on running failure of BAC suggested that particle size distribution could have effect on operation of BAC filter. Running problem occured when the ratio of particle with size greater than 0.8 mm was less than 37% and K80 was more than 3.6. The particle size decreased and asymmetrical coefficient increased over time, and it led to a high head loss and low water yield of BAC filter. But the filter material still had effect on water treatment. Removal of fine carbon 40 cm below the surface could be used to resume operation of the filter colume.