Assessing the effectiveness of iron - coated bottom ash in removing arsenic , manganese and iron from groundwater

Abstract

Arscnic removal USing iron-coated botlom ash (ICBA) IS a novcl proccss of removing arsenic fi'om groundwater invcntcd by rcscarchcrs at Lawrence Berkeley International Laboratory, USA. Adsorption/co-prccipitation mcthod has been cmploycd in this ncw technology. The prcscnt study involvcs development of a community-based trcatment unit and investigations relating its performance using iron coated bottom ash (lCBA) in reducing the clcvatcd Icvels of arsenic, and other contaminants such as iron and mangancse from groundwater of Bangladesh. In this rcsearch, the samples have been collccted for batch analyscs from Besgao village, Sreenagar, Munshiganj, an arsenic affected area which has been the subject of several arscnic rclatcd investigations for the last five years. From the investigations performed in the laboratory scale, an ICBA dosage of 4 giL and coagulant dosage of 0.25 gil have been found to be optimum for good arsenic removal and therefore selected for subscquent batch cxperiments. ICBA seems to work better for pH levels 5.71-8.78 for synthetic groundwater samples. The higher the initial pH, the higher is thc arsenic removal. Interference of phosphate content with arsenic removal has been obscrved to increase with the increase in phosphate concentration. Further investigations are necessary to better understand the mechanism of phosphate with arsenic adsorption using ICBA. Results from the investigations performed with the community based tre~tment unit show that the performance of the unit varies with the flow rate. A flow rate of 100 Liters per hour provides the best pcrformancc. The lower the initial arsenic concentration, the betier is thc pcrlormancc of thc prototype in reducing arsel11c concentration in the treated water below the Bangladesh drinking water standard. Performance of the unit in removing inevitable bacteriological contamination is enhanced when there is low level of contamination. For higher TC/FC, it takes around eight days to attain the rcquired bactcriological quality of water. Presence of Iron-Related Bacteria (lRB) seems to change the performance of ICBA in removing As, Fe and Mn by attacking the adsorptive bonds between the contaminants and the ICBA. The number of IRB population has been observed to be as high as 1,40,000 cfu/ml in thc raw groundwater. This number can be reduced to 9000 efu/ml after trcatment with ICBA and chlorination dosc of 1.55 mg/L, but cannot bc completely rcmoved within a rcasonablc limc. It is important to mention that the number of TC/FC present in the same water is also very high. In that case, presence of high IRB may have some contribution in giving false notion of prcsencc of such high TC/FC. Arsenic sludge ii'om iron coated bottom ash does not allow arsenic to Io::achout under low pH environment. However, very high pl-! conditions ('" 11) can cause leaching of arsenic from the sludge. Both arsenic and cadmium contents in raw wastes and leachates arc within the guidcline practiced for surface disposal according to US EPA (1995). For groundwater having low initial arsenic concentration (around 200 ~g1L), low initial manganese content (S O.I25 mglL), and low bacteriological contamination, a hundred liter per hour prototype can be successfully implemented in treating the groundwater to achieve the Bangladesh drinking water standard. However, aesthetic quality of the treated watcr is not possible to obtain for high level of iron content (> 6 mg/L) without incorporation of a filtration unit. Howcver, acccptability of this prototypc system to the community could not be ascertained as the prototype lu; not been installed in the field for use of the community.