Development of a Low Cost Household Level Biological Arsenic-Iron Removal Unit

Abstract

The urban and rural water supply system in Bangladesh is mainly dependent on groundwater. Widespread arsenic contamination and presence of elevated level of iron in groundwater are the major water quality problem in Bangladesh, Thousands of people are reported to have already symptoms of severs arsenic poisoning and several millions arc at risk of arsenic, contamination from drinking tubewell water. A few number of costly household level Arsenic and iron removal units are available in the contaminated areas but most of them are chemical dependent and complex in operation and maintenance. The socio-economic conditions of Bangladesh demands low-cost treatment systems that could be implemented in the rural areas at household levels. Although a few household level arsenic removal units have been developed and tested, little -attempt has been made in the development of a low cost biological type arsenic-iron removal unit. Considering the above points, a low cost bio-physicochemical treatment unit has been developed al laboratory scale for simultaneous arsenic and iron removal from groundwater. The biological fixed bed reactor using coconut husk along with iron-matrix, charcoal and sand filtration have combined the bio-physicochemical removal processes in o single system. The unit was developed by using locally available materials in Bangladesh. The developed unit consists of three buckets where arsenic-iron contaminated raw water was poured into the first one. In this bucket bio-oxidation took place. Arsenic-Iron concentrated raw water was oxidized by the bacteria. The bacteria were produced on coconut husk bed and form small particles by sorption onto Fe(OH)3. 111 second bucket comparatively larger flocculated particles precipitated and settled at the lop of the chamber nod the removal of precipitated particles through sorption onto iron ox hydroxides. Additional adsorption of escaped arsenic from the first bucket was done on the iron matrix layer in the second bucket. Other fine and coarse particles precipitated on charcoal and coarse sand. Final removal of bacteria and other fine particles were accomplished in the 3rd bucket TI1is bucket consists of simple methodological technique of slow sand filtration under submerged condition i.e, stable bio¬ film slime layer. Following the above technique, detail laboratory analysis nod tests were carried out for nine different ratios of arsenic-iron concentrated synthetic raw water, Considering different hydro¬ geological conditions, modifications were made to the developed unit for field applications. The modified units were then installed and tested in different water quality conditions at the field level. The main findings drawn from this test were as follows: (i) The raw water with arsenic concentration up to 500 ppb was treated with the laboratory and field treatment units satisfying Bangladesh standards (50ppb) without using any chemicals; (ii) Maintaining a face velocity of 0.5 m3m2-hr, appreciable iron removal efficiency over 90'>/o was achieved through the treatment unit; (iii) No sign of Total Coliform were detected in the treated water produced by the unit. It appeared that the units performed consistently well in eliminating bacteria; (iv) Some selected water quality parameters of treated water (pH, Turbidity, Color, Mn, DO, EC) were determined at random basis and they were found within the acceptable limit of Bangladesh standard: and [v] The operation and maintenance of the developed treatment units are simpler and more users friendly. It was observed that the clogging of the units were occurred over six months for most of the cases, Clogging of the units was varied for different iron concentrations of the raw water. The final finding was observed that the unit produced sparkling clear water with no arsenic and iron for continuous duration of six to ten months without any maintenance.