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For many developing nations, biogas has traditionally been used for household cooking and lighting. Methane (CH 4) content in biogas has to be increased by removing incombustible carbon dioxide (CO 2) and potentially corrosive constituents such as hydrogen sulphide (H 2 S) and moisture. This study set out to increase biogas from 55.8% CH 4 , 43% CO 2 , 0.85% oxygen (O 2), 75.1 ppm H 2 S to >80% methane and non-traceable H 2 S without enhancing raw biogas pressure. By using a single scrubber column and varying water scrubbing system operating parameters of packing material type, packing depth, water and gas flow rates, appropriate parameters for achieving the above objective were determined. The experiments were carried out at an average digester pressure of 1.0589bar. Results show that packing a column with steel-wire mesh to a depth of 0.4m increases the volumetric percentage of CH 4 in biogas to >80% for water to gas flow rate ratios 1.9 and above. Increasing the packed depth to 0.8m increases volumetric percentage of CH 4 in biogas to 80% at a lower ratio of 0.7. This increase in packed depth resulted in an improvement from 1800 litres to 700 litres of water for every m 3 of raw biogas upgraded. However, to achieve >80% CH 4 in marble packed columns of similar depths, the water to gas flow rate ratio has to be raised above 2.5.

Peri-urban fish farms with limited access to open natural water bodies draw fresh water from urban water supply and dug wells, which is unreliable and costly. Reuse of fish pond effluent is also limited by high ammonia concentration (> 0.3 mg/L) that renders water toxic and is stressful to fish. Despite the existence of several fish effluent treatment methods, not all may be appropriate for a particular location. This review article therefore examines the various fish effluent treatment methods to aid selection of the most suitable one(s) for peri-urban areas. The key parameters considered in their comparison were: initial, operational and maintenance costs; ammonia removal efficiency; energy consumption and land requirement. The effluent treatment methods are both conventional and non-conventional. Despite a slight higher treatment efficiency and less space requirement by conventional methods, they mainly require reliable power supply for continuous running, highly skilled labor for operation and maintenance leading to high operational costs. In addition, their investment costs are higher than non-conventional methods, hence not widely applied in developing countries and majority have broken down. On the other hand, non-conventional methods such as constructed wetlands are widely in use for treating effluent mainly due to their cost effectiveness and no or little energy requirement. Constructed wetlands were found most suitable bio-filtration system for treating fish effluent because they are cost effective, require less skilled labor and still have better effluent treatment though space required is slightly more. Vegetables (lettuce, collards, etc.) have potential to grow in constructed wetlands thus form vegetable-based bio-filtration units which serve not only as bio-filters but also provide additional sources of nutrition and income. This review indicated limited information on the appropriate size and performance of vegetable-based bio-filtration unit utilizing indigenous vegetables and recommended further research to explore the idea.

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The increasing Uganda's urban population growth has led to limited space coupled with high cost of living, thus making it difficult for the urban poor in congested areas to afford fish protein hence poor nutrition among the low income earners. Therefore this study was conducted to evaluate the performance of collard based bio-filtration system for filtering fish tank effluent for re-use in congested peri-urban areas. Field physical-chemical parameters (ammonia, nitrate, dissolved oxygen, temperature and pH) were measured at various bio-filter lengths in the effluent from both collard based and GBF (Gravel Based Bio-Filter). Differences in mean ammonia and nitrate levels at various lengths were analyzed using one-way ANOVA at p = 0.05. Ammonia levels were significantly reduced (p < 0.05