Development and testing of an on-site domestic grey water treatment system using crushed bricks and maize cob charcoal as treatment medium

Abstract

Developing countries have low levels of access to piped water supply and sanitation. Most household in rural and poor urban areas lack water connections or wastewater disposal systems. Water is fetched from distant sources mostly by women and children. Recycling and reuse of water is an option for the partial reclamation of the value invested in the water and reducing the effluent load on the open drains that serve for sewers. The main objective of this study was to develop and test a biological household level greywater treatment system using locally available materials to a level of reusing the treated water as an alternative source for non-portable uses within communities. The specific objectives were; (i) to design and fabricate an appropriate greywater treatment system fit for treating greywater from kitchen, (ii) to run a lab-scale treatment technology assessment for the designed system to evaluate the performance of crushed bricks mixed with maize cob charcoal used in the designed system as the treatment medium and (iii) to evaluate the system run time for maximum performance. The study used greywater collected from Moi University Ngeria students’ cafeteria kitchen that was passed through a test unit with anaerobic tank filled with wood charcoal and a series of five slanted filter beds stacked above each other and filled with treatment media of crushed bricks (B) and maize cob charcoal (C) both of mean diameter 10mm ±2 mixed in a C:B ratio of 1:3. A similar arrangement was also set up for a control with only crushed bricks as the treatment media. The flow through the units was by gravity at a domestic freshwater demand of 72 l/head/day. Sampling for both influent and effluent from the anaerobic chambers and filter beds were collected weekly and analysed for selected water quality parameters characterized for domestic greywater including BOD 5 , NH 4 , TN and TP. It was observed that effective removal of organic matter (BOD 5 ) in both systems began one week after start up. The anaerobic chambers on average removed 55.1% of the organic loading in the greywater by reducing the BOD 5 from 544.3mg/l in the raw greywater to 231.2mg/l. The water quality improvement for the test unit in the removal of the parameters were: BOD 5 - 544.3 to 6.1mg/l (99%), NH 4 – 1.3 to 0.49 mg/l (62%), TN – 32.7 to 3.6mg/l (89%) and TP – 6.5 to 0.6mg/l (90%). For the control unit in the removal of these parameters were: BOD 5 – 544.3 to 21.8mg/l (96%), NH 4 – 1.3 to 0.6mg/l (54%), TN – 32.7 to 3.5mg/l (89%) and TP – 6.5 to 1.0mg/l(85%). The BOD 5 concentrations recorded in the effluent from the test system was below 10mg/l with the lowest at 1.2mg/l in the 5 th week for the first 16 weeks indicating run time of 16 weeks of effective operation. In the 17 th week, it recorded the first high of 13.0mg/l which kept on rising to a maximum of 18.9mg/l in the 22 nd week. Analysis of the results from the two units indicated a better performance of the test unit in removing the measured parameters which could be associated with the incorporation of maize cob charcoal in the crushed bricks due to the porous nature of charcoal which provided a suitable habitat for microbes that helped in clarifying grey water biologically. The test system was effective for 16 weeks when it was operating below 10mg/l recommended by WHO standards for lawn and flower watering, dust control among other non-portable uses.