A Study Of Powdered Activated Carbon For Removing Pollutants From Huangpujiang Raw Water Samples

A wide variety of organic and inorganic pollutants have been found in most Chinese cities'water sources. Water quality has deteriorated substantially in recent years due to presence of many toxic and hazardous chemicals and other pollutants in the raw water streams. There have been more incidents of accidental pollution of raw water. According to the new drinking water quality standard (GB5749-2006), a variety of trace organic pollutants will have to be removed by proper treatment of the raw waters. Conventional water treatment plant employing coagulation-precipitation, filtration and disinfection are unable to remove all the harmful pollutants of the raw water to meet the human health requirements. There is an urgent need to develop a cost effective solution. Powdered activated carbon (PAC) adsorption is an attractive raw water treatment technology because PAC can be introduced to the existing water treatment system to remove trace organic contaminants, disinfection by-products and precursors, artificial organic compounds, other toxic and harmful substances. Indeed PAC has increasingly been utilized for treating raw water in China and most developed countries abroad.This research was conducted to correlate the PAC's four adsorptive capacity indicators (phenol, iodine, methylene blue and tannic acid numbers) with its pore structure (specific surface area and pore volume vs. particle size distribution) as well as its effectiveness in removing the raw water's organic constituents (CODMn, TOC, UV254), two accidental pollutants (nitrobenzene and diesel oil) and an endocrine disruptor (bisphenol A) often found in the Huangpujiang raw water samples for a total of 11 PACs of different raw materials and activation methods. Many series of the adsorption rate (pollutant concentration decline curves of a batch reactor following the addition of a dose of PAC) and equilibrium adsorption capacity experiments were conducted to investigate water treatment performance of those PACs by adsorption and/or with coagulation-flocculation-sedimentation. The experimental results show that tannic acid number can indicate the effectiveness of PAC in removing UV254 substtances and that the order of PACs'phenol number was the same as the order of their adsorption capacities for nitrobenzene.Simulating an actual water treatment plant operation, the static model adsorption experiments were conducted to investigate the effects of PAC dosing location, coagulant/PAC type and dosage on the pollutant removal from the raw water. The best location of PAC addition was the water intake well; the porformance of polyaluminum chloride was better than polymeric ferric sulfate; 5# PAC performed the best overall while 4# PAC was most effective in removing nitrobenzene and bisphenol A; bamboo PAC was the best in removing disel oil and likely other petroleum pollutants. The results of the simulation adsorption treatment have verifed the conclusions of the adsorptive capacity experiments employing the same PACs.