Technologies for Arsenic, Fluoride and Iron Removal
2.2 HOUSEHOLD LEVEL TECHNOLOGIES
2.2.3 Household Level Technologies for Iron Removal
Technologies for Arsenic, Fluoride and Iron Removal
h intervals. High fluoride groundwater of 4 mg/L could be reduced to less than 1 mg/L using the filter conforming to WHO standards for fluoride (WHO, 1984).
Technologies for Arsenic, Fluoride and Iron Removal
62
hydraulic loading was adequate to serve a population of 250 at a rate of 10 L water per person with a 10 h operation every day. The unit comprised of three chambers (HP- IRP, 2004). Hand pump water was sprayed over an oxidation chamber. The aerated water flowed over baffle plate to the sedimentation chamber after it passed through flocculation chamber. The water then passed through plate settlers to the filter from where the filtered water was drawn through a tap after chlorination. The Fe(III) precipitate settled as sludge and required periodic scouring depending upon raw water quality and quantity drawn. No chemical was required except chlorine solution for disinfection. The plant required cleaning twice a month. The capital cost of the unit was approximately Rs. 15,000 while operation and maintenance costs were low.
A small version of an iron removal unit was attached to a hand pump tube well and was used where groundwater contained an excessive amount of iron (Ahsan, 2004).
The treatment method consisted of aeration, sedimentation, flocculation and sedimentation in a roughing filter and final filtration. The water from the hand pump tube well was passed through a slotted horizontal PVC pipe and fell into the cubical structure. The structure consisted of three chambers. Water from the slotted pipe fell into the first chamber and aeration occurred with partial sedimentation. Water from the first chamber then entered the bottom of the second chamber which was an up-flow roughing filter with coarse aggregates (20-30 mm). Flocculation sedimentation occurred at this stage and iron hydroxide micro-flocs grew in size with most of them settling onto the coarse aggregates. The partially filtered water then overflowed into the third chamber consisting of a bed of coarse sand or small aggregates and a final down flow filtration took place. The filtered water was delivered through an underlying compartment and pipes. During iron removal process, arsenic was also removed by adsorption and co-precipitation. The iron removal units required regular washing to maintain them in a proper working condition. Where the iron concentration was over 10 mg/L, partial cleaning was required every 7-10 days. Partial cleaning was done by scraping the top layer of the smaller grain filter media in the third chamber, opening all washouts and pouring two to three buckets of water over each chamber. The scraped filter media was cleaned and replaced in position. Complete washing was required once a month.
TH-945_05610401
Technologies for Arsenic, Fluoride and Iron Removal
2.2.3.3 FINNIDA Square Type Iron Removal Plant
The Finnish International Development Agency (FINNIDA) square type filter was developed in Sri Lanka in 1989 (Hartmann, 2001). The special features of the FINNIDA square type filter were simplicity of design and possibility of in-situ economical construction. Operation and maintenance were easy. FINNIDA square type filter units were installed at hand pump wells where the groundwater had excessive iron content. It could be built mostly of locally available fired bricks of size 18 cm × 9 cm × 6 cm. The reinforced concrete lid was made in three parts, and each part was fitted with handles facilitating easy lifting. The square filter unit was subdivided into two chambers. The inner chamber was like a tapered trough formed from concrete slabs, and it was packed with filter media having a grain size in the range of 1 to 3 cm.
Incoming water from the hand pump outlet flowed through a 7.5 cm diameter inlet pipe and then entered the chamber near the floor through a pipe of 5 cm diameter, which had holes for discharging the inflow along length of the trough. When this inner chamber was full, water spilled out into the outer chamber over sharpened weirs on three sides of the inner chamber. There was a washout port to allow easy draining of the inner chamber for cleaning purposes. The second chamber contained wood charcoal and sand for filtering this water. There was a horizontal pipe with holes in it near the floor of this outer chamber which collected the water after it had filtered down through the sand and charcoal. There were also two washout ports used for frequent cleaning of the filter media.
2.2.3.4 Domestic Iron Removal Unit
The unit developed resulted in production of iron free water. The soluble divalent ferrous ions were oxidized to higher valent states during passage of water through the unit and thus got converted to insoluble precipitates. These precipitates and any other insoluble forms of iron were removed during filtration through the filtering medium (DIRU, 2009). The unit had been tested in the field with water containing more than 15 mg/L iron in soluble ferrous form and 140–470 mg/L carbon di-oxide. Iron levels were reduced to almost zero level.
Technologies for Arsenic, Fluoride and Iron Removal
64 2.2.3.5 Iron Removal Systems
Ion Exchange India limited had developed an iron removal system in which a catalytic media adsorbed dissolved iron onto its surface and/or oxidized it and got removed through settling (IRS, 2003). The system could filter 400 to 25000 L/h (IRS, 2003). The media of the iron removal system did not undergo any chemical change.
The system was very compact and economical and did not require any electricity for its operation. Only alum was needed for regeneration of the exchange media. The system was sturdy and did not require special skill to operate. The system was claimed to be maintenance free.
2.3 AVAILABLE DESIGN APPROACHES