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On-site Grey Water Treatment by Membrane Filtration
Mudalungu Edwin 12 , Tomoaki Itayama 13 , Saul Namango 1, Job Kosgei 1
1. Moi university 2. LAVICORD project, 3. Nagasaki University.
Objective:
Not more than 59% of the total population in Kenya access portable water and 10% of the daily deaths is reported to be as result of waterborne diseases . More of the deaths occur in informal settlements and rural areas .(UNICEF 2007). Access to the portable water is hampered as a result of ; pollution of water sources, limited fresh water sources, and lack of enough water treatment and supply infrastructure. In order to improve accessibility to portable water , research on grey water treatment for non portable re-use was reviewed .We conducted an experimental study on membrane filtration of grey water ; pre-treated by slanted soil unit filled with filter media made from locally available materials.
Material and methods:
The experiment was carried out at the school of Engineering Moi university (Eldoret) from May to December The study was designed to have two similar, hollow fiber microfiltration membrane (MF) set ups each 36cm in length with filtration surface area of m2. Each membrane was inserted and fastened in a one millimeter silicon tube so that there was a complete vacuum at the filtration side so as to have an effective Trans-Membrane pressure .
The feed side to one of the membrane was grey water pre-treated by filter media of mixed bricks and charcoal (targeted experiment ) , while feed for the other membrane set up was grey water pre-treated by filter media of bricks alone ( control experiment).
Filtration was achieved by siphoning through a constant head of 90cm, while filtration flux was enhanced by daily backwashing for 30minutes with product water at 92 cm reverse head. Membrane chemical cleaning was done weekly by soaking the membranes in a 3% concentration of sodium hypochlorous solution for twenty four hours and later soaking in Milli- Q water for 15minutes.
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A photograph of slanted soil system (pre-treatment set up )
A photograph of membrane filtration set up
Trans-membrane pressure-pressure exerted on the membrane pores to facilitate filtration process- The higher the pore blockage the higher the TPM for that particular situation. Operation with constant TPM results to reduced flux during fouling
Filtration flux(l/m2.h)- volume of permeate passing through unit square meter of the membrane per given hour –higher filtration flux records high frequency of membrane fouling while the opposite is true low filtration flux for same influent water quality. Operation with a constant filtration flux results in increased TPM when membrane fouls.
Results and discussions:
Membrane treatment was fairly good as the target experiment attained impurity reduction of % for five day biochemical oxygen demand (BOD5 ),94.36%for turbidity ,99.48% for total bacteria and 99.85%,for total suspended solids( TSS) .
The control experiment attained average impurity reduction of 87.2%, 93.08%, 99.56%, and 99.91% for biochemical oxygen demand, turbidity, total bacteria, and total suspended solids respectively. pH for the target and control membrane filtration experiments reduced from average 9.03 to 7.37 (17.58%) and from 9.3 to 7.5 (18.51%) respectively.
In the entire period, the targeted experiment had a relatively higher average maximum filtration flux of L/M2.H unlike 58.61L/M2.H for the control experiment. Respective average minimum filtration flux was L/M2.H and 41.9 L/M2.H meaning there was more membrane pore blockage due to irreversible fouling for the control than for the target experiments during the study.
Conclusions &Recommendations:
From the experimental results ,the filtrate is of good quality and meets WHO non -restrictive waste water reuse standards . With a typical membrane ,the fouling regime is expected to change depending on pre-treatment method , operation conditions , location and the water quality of feed .
It is recommended that ; 1) Further work to be carried out using a different membrane module. 2) Different cleaning agent to used for membrane chemical cleaning for comparison purposes. 3) Investigation to be done to determine the nature of dominant foulant material in a similar membrane filtration study.
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Minimum fluxes attained in both filtrations before next chemical cleaning.
BOD 5 fluctuations during the study
Maximum fluxes attained in both filtrations after every chemical cleaning.