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A study was undertaken to remove colour from a kraft mill's treated effluent in Kenya and determine the suitability of phosphate rock to replace wood ash during the electrochemical process. The electrochemical method alone, electrochemical combined with alum (ELCAL), wood ash leachate (ELCAS) and phosphate rock (ELPHOS) solutions at a rate of 165 to 1000 g/m3 were tested. Effluent characteristics were determined after complete removal of colour. Same reduction rates of TS (85%) and TSS (89%) were recorded by ELCAS and ELPHOS. However, ELPHOS removed more COD (86 to 91%) and more BOD (85 to 92%) than ELCAS. Furthermore, the pH of ELPHOS treated solution was 9.3, within the Kenya Local Government's allowable limit. Power reduction with ELCAS and ELPHOS varied between 53 to 73% and 49 to 69% respectively but the difference was not statistically significant. Overnight aeration further improved the quality of ELCAS and ELPHOS treated effluent, reducing BOD and COD values to 0 mg/l. ELPHOS cost ($0.29/m3) was nevertheless three times higher than that of ELCAS ($0.10/m3), mainly because of free wood ash. ELPHOS did not also increase effluent phosphorus. It was therefore recommended that various ways be explored in making ELPHOS more economical to replace ELCAS.

The potential of four aquatic macrophytes for treatment of wastewater in constructed wetlands was investigated in bucket mesocosms at Pan African Paper Mills (E.A) Limited. The buckets were operated as semi-continuous batch reactors with reversed vertical flow for a period of 3 months. Four treatments were applied involving two hydraulic retention times (HRT) and two wastewater concentrations. Plants appear healthier and greener in treatments at HRT5 than at HRT10. Cyperus immensus and Typha domingensis had higher biomass gain compared to the other two species. Plant nitrogen and phosphorus content, based on dry weight, was lower at the end of the experiment than at the beginning in all treatments for all species The removal efficiency achieved for COD ranged from 10 to 55% for planted buckets at HRT5 and 15 to 65% at HRT10 for similar buckets. The mean percentage COD removal in unplanted buckets was significantly lower than in planted ones. TSS removal efficiency ranged from 44-86%. Buckets planted with Typha exhibited the highest removal efficiency in all treatments. Those at HRT5 showed significantly higher removal efficiencies than those at HRT10 for all species. The results indicate that the plants are suitable for use in constructed wetlands for treatment of the wastewater provided the appropriate treatment is applied.