A Study of the low cost filter media to be used in the modification of an ancient urine filtration system in Sri Lanka

Abstract

Algal blooms have been identified as one of the most devastating issues in the urban water bodies. Enrichment of nutrient such as Nitrogen, Phosphorus and Potassium stimulate algal blooms. Even though the fraction of urine in domestic waste water is less than 1% of the total volume while human urine contributes 80% of the nitrogen and 55% of the phosphorus in urban water bodies. Hence, most of the countries have adopted modern urine treatment technologies. Nevertheless, most of the urine streams have still been diverted the urban water bodies. In ancient Sri Lanka, a simple pot system had been used to filter urine before discharging into soil. Low cost materials such as sand, charcoal, calcite had been used as filter media in the pot system. This research focuses on investigating the feasibility of using such filter materials in a modern low cost filter for urine filtration. Alternatively brick powder was selected owing its higher adsorption capacities. Being a mixture of hundreds of organic and inorganic compounds, urine is quite sensitive to the variations of its pH value. It was noted that at elevated pH values (especially after 8.5 of pH) light amber colour turbid clouds are formed in urine. Increase of turbidity (suspended solids in other terms) improves the filtration efficiency of sand beds. Therefore the minimum calcite bed height that increases the urine pH above 8.5 was investigated. Sand samples collected from various locations in the country were analysed for their suspended matter (TSS) removal capacities. It was found that TSS removal of sand shows direct relationship to the sand particle size. Naththandiya silica sand which has considerably small mean particle size (703.97 𝜇𝑚) shows the highest TSS removal. Charcoal prepared from Kohomba branches shows the highest adsorption capacity (Iodine number 181.82 mg/g) among 12 charcoal types investigated. Breakthrough curves for sand, brick powder and charcoal was drawn using both urine and urea. Simultaneously, batch experiments were carried out both for brick powder and Kohomba charcoal. Langmuir adsorption isotherm model is best fitted for both brick powder-urea and charcoal-urea systems.