Composite samples of sludge obtained from a textile factory were characterized for their pollution characteristics using some parameters of interest; pH, solids concentration, oxygen demand, nitrogen, phosphorus, total bacteria counts etc. The analysis revealed that the sludge has high pollution potentials and therefore needed treatment before disposal to the environment. The ratio of chemical oxygen demand, (COD) to that of biochemical oxygen demand, (BOD) was 3.08; meaning the sludge has high substrate biodegradability. Samples were subjected to mesophilic anaerobic treatment at the temperature of 352C. The method achieved solids reduction of 61% total solids, 68% settleable solids and 51% volatile solids and a total bacteria reduction of 99.99%. The reduction in BOD and COD were 89% each. Nitrate and phosphate were found to reduce substantially thereby preventing eutrophication due to undesirable nutrients. The anaerobic treatment was found to have an additional benefit of producing biogas (methane and carbon (IV) oxide) which if harnessed may be used as fuel.
Key words: Textilee, mesophilic anaerobic treatment, pollution, digestion, eutrphication, sludge.
Increasing urbanization and industrialization have resulted in a dramatic increase in the volume of wastewater produced around the world. Textile industries are large industrial consumers of waters as well as producers of wastewater. Tightening environmental standards have meant that much of these wastewaters have to be treated before it can be safely discharged. The wastewater treatment step concentrates the various pollutants in the wastewater into sludge, normally containing between 1 and 2% by weight dry solids (Priestly, 1991). Because of the dramatic increase in volume of wastewater treated large volume of sludge need to be disposed of in an environmentally safe manner. There is therefore the need to effect proper treatment to sludge before disposal or reuse.
The goal of all biological wastewater treatment systems is to remove the non-settling solids and the dissolved organic load from the effluents by using microbial populations. Biological treatments are generally part of secondary treatment systems. The microorganisms used are responsible for the degradation of the organic matter and the stabilization of organic wastes. Amongst the various practical biological treatment methods, anaerobic digestion is often the most attractive option for treatment of sludge due to the following advantages; a high BOD and COD reduction, production of energy as biogas, production of a bio-fertilizer, small production of already stabilized biological sludge that can be use as a nutrient, lower capital cost, beside all these inherent advantages, in Nigeria, climatic conditions are favourable and there is a considerable capacity to develop and optimize the process in research institute and universities.
In the recent times, efforts have been geared towards the treatment of domestic and industrial wastewaters while the sludges associated with them are merely dumped untreated into the environment. Many of the steps taken to treat wastewaters results in the concentration of pollutants into sludge (Priestly, 1991). Sludge therefore becomes unstable, putrescible and pathogenic. Sludge must therefore be treated before disposal or reuse in order to remediate our environment. This work is focused on proper treatment to sludge from a textile factory using anaerobic digestion method.
Anaerobic digestion has been reported to achieve a reasonable reduction in the organic content of sludge. The main products being methane gas and carbon (IV) oxide (David, 1990; Asia, 2000).