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The requirement of color removal has promoted the research in this field. However, there is still a lack of understanding of colour problems. In this paper a literature review is made to assess the information on color removal and need for systematic evaluation of the results is emphasized. Experimental studies are conducted on the textile dyeing wastewaters applying chemical precipitation, chemical oxidation, adsorption and their combination. Results of the study are evaluated and discussed within the context of a systematic approach.

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In this study, the theoretical basis and limitations of magnesium ammonium phosphate (MAP) precipitation are investigated and experimentally tested for leather tanning industry. The MAP precipitation is applied to leather tanning wastewaters for both segregated flows containing high ammonia concentrations and combined flows. Segregated flow treatment on smaller volumes of wastewater provided an ammonia concentration of down to 150 mg l−1 NH3-N. The resulting ammonia concentration of MAP precipitation on combined wastewater is at the level of domestic wastewater which eliminates the need of further nitrogen removal in the biological treatment and provides an effluent quality acceptable for the public sewer.

This study investigates the applicability of hydroxide precipitation to complexed metal wastewaters using inorganic cations that may function as ligand sharing agents. Within this context Ca2+, Fe2+, Fe3+, Mn2+ and Mg2+ cations with the metals Cd and Cu and EDTA and NTA as ligands are used to define the systems for which theoretical and experimental evaluations are made. Results indicate that calcium is the only cation that effectively binds the ligands that makes it possible to apply the hydroxide precipitation. Fe2+ and Mn2+ are not effective due to their rapid oxidation. Mg2+ is found partly effective but may not be adequate for pretreatment purposes.

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Human urine is a source of nutrients and has a significant potential for recycle of nitrogen. Recently, much research focused on separate collection and treatment of human urine. Recovery of nutrients from human urine requires hydrolysis of urea into ammonia and subsequent removal of ammonia and sometimes phosphorus. This study attempted to evaluate urea hydrolysis of human urine in both untreated fresh samples and urease added urine samples. Recovery of nutrients by struvite precipitation on pre-hydrolysed samples was also assessed on undiluted and 1:1 diluted samples. Results of urea hydrolysis on untreated urine samples indicated that the process was slow and pH exerted a significant effect on the process. No hydrolysis occurred above pH 10. From pH 2 to 7.5, 25% of urea could be hydrolysed in 30 d. Urease added hydrolysis with the enzyme doses 25-49 mg L(-1) was a rapid process providing complete conversion into ammonia in 1.5 h. Struvite precipitation conducted on enzyme hydrolysed urine sample proved to be an efficient process and ammonia removals up to 95% were obtained. Struvite precipitation also provided 50% organic nitrogen removal.