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Bangladesh Textile Today - A Comprehensive Publication for the Textile & Apparel Industry
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Production of bio-gas from textile sludge by anaerobic digestion, a sustainable eco-friendly sludge management method

The project has won the champion in Textile Talent Hunt 2013. This project paper is being published in two parts. This is the first part of the paper and the last part will be published on July 2014 issue. Abstract: 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) were 3.08 [1]; meaning the sludge has high substrate biodegradability. Samples were subjected to mesospheric anaerobic treatment at the temperature of 35°C along with sodium bi carbonate. The anaerobic treatment is termed to have producing biogas (methane and carbon di-oxide) which if harnessed can be used as fuel. Biogas from textile sludge then can be used as household cooking, car fuel & can produce electricity with the help of gas generator. Electricity can be generated in larger amount with the bigger treatment system and larger amount of sludge. In this work bio-sludge was collected from a factory located in Gazipur & initially confirmed the production of biogas in lab scale. After that bio-sludge was used to prepare biogas in a plant at Bhairab, Kishoregonj following standard methods and this biogas has been utilized for cooking foods of a family. There are several options of sludge management such as, Incineration, Composting, Building Material (Bricks & Cement Manufacturing), Wet land filling, and Biogas production. Considering Bangladesh’s situation biogas production from textile sludge could be a sustainable eco-friendly technique.   1. Introduction 1.1 Project Description The hypothesis of this research is anaerobic digestion of textile sludge will lead to production of biogas. The working method is an anaerobic digestion of textile sludge with a standard method. Completion of lab scale parametric studies will determine biogas production, with the ultimate goal of Production biogas from the textile sludge in a larger scale.  Fig 1: Operation Flowchart 1.2 General Interpretation: Biogas, as a renewable energy, can be produced from a variety of organic raw materials and utilized for various energy services, such as heat, combined heat and power or as a vehicle fuel. Biogas can be produced by anaerobic digestion or fermentation of biodegradable materials such as biomass, textile sludge, manure, sewage, municipal waste, green waste, plants material and energy crops. Emphasis is laid on sludge from textile wastewater treatment plants in this paper. As we know, large amounts of waste activated sludge, containing organic and mineral components, are produced by industrial wastewater treatment plants. Sludge handling represents a bottleneck in wastewater treatment plants, due to environmental, economic, social and legal factors. If handled properly, sludge can be a valuable resource for renewable energy production and a source of nutrients for agriculture. [3]. Bangladesh is heavily involved in textile production and export. A lot of textile mills were established in the country in last two decades. A large number of these mills generate and discharge waste waters. It was reported by the various organization and monitoring authority that the pollution of the rivers and canals in well above their acceptable level. Various agencies are trying to safeguard the clean environment. Bangladesh Government has already issued various forms of warning and red alerts to the concerned industries. A lot of textile wet processing industries have already installed effluent treatment plants (ETP) and many of them are at various stages of installing ETP's. [2] There are various types of textile wet processing plants e.g., the woven dyeing plants and, Knit dyeing plants, Yarn and garments Dyeing plants. The technique for dyeing of textile materials mainly depends on the type of fibre. Some widely used fibre that are produced and exported from Bangladesh includes Cotton, wool, silk, linen, polyester, nylon, viscose, acrylics etc. These fibres can also be classed into two main classes‘ e.g. Natural fibre-those produced naturally e.g. cotton, jute, wool silk etc. & Synthetic fibre- man-made fibre that are produced from petroleum product. Dyeing of the above mentioned fibres are somewhat different and each of them requires a different class of dye. Different dyestuffs require different types of chemicals and auxiliaries to apply them into the fabric or textile product. As a result the characteristics of the textile waste water vary significantly. Due to variation of characteristics, textile waste water requires various types of techniques to treat them. [2] Even though ETP techniques are quite convincing so far to treat the textile waste successfully, ETPs’ by product sludge remains as key environmental threat. 1.3 Sludge Management Options a. Incineration. b. Composting. c. Building Material (Bricks & Cement Manufacturing) d. Wet-landfilling. e. Biogas production. 1.3. a. Incineration. Incineration of sludge involves the combustion of organic substances contained in waste materials.[32]Incineration and other high-temperature waste treatment systems are described as "thermal treatment". Incineration of waste materials converts the waste into ash, and heat. There are disadvantages like, formation of dioxin gas in the process, presence of other health Hazards and cost is of the process very high. Fig 2. Sludge incineration 1.3. b. Composting Composting is an aerobic bacterial decomposition process to stabilize organic wastes and industrial sludge (compost). Compost contains nutrients and organic carbon which are excellent soil conditioners. Composting takes place naturally on a forest floor where organic materials (leaf litter, animal wastes) are converted to more stable organic materials (humus) and the nutrients are released and made available for plant uptake. The process is slow on a forest floor, but can be accelerated under optimum conditions. After composting toxicity may coverts to food chain through plants, application process may impose human health hazard. Fig 3. Sludge composting 1.3. c. Bricks & cement manufacturing Now-a-days textile sludge is being used for producing building materials such as bricks, cements etc. Utilization of textile sludge on this way has some adverse effects especially when the sludge has high salt content, the bricks may cause damage of the plaster of the wall several years later. Cement manufacturing process includes sludge incineration and may cause health hazard during its application. Fig 4. Bricks from sludge   1.4. d. Wet-landfilling. Textile sludge can be used for wet land filling purpose, but on the perspective of Bangladesh it is not a sustainable method for sludge management because it imposes threat for aqueous life and the land cannot be used for any other eco-friendly purpose. Fig 5. Wet land filling by sludge   1.3. e. Biogas production. By using textile sludge production of biogas or bio methane is a sustainable eco-friendly method for sludge management. With anaerobic digestion method sludge can be treated and produce biogas from that and residual can be used for agricultural purpose. Fig 6. Biogas from sludge   1.4 Categories of Sludge (Biosolids) A. Class A Biosolids B. Class B Biosolids C. Class C Biosolids 1.4. A. Class A bio-solids Class A Biosolids is a designation for dewatered and heated sewage sludge that meets U.S. EPA guidelines for land application with no restrictions. Thus, class A biosolids can be legally used as fertilizer on farms, vegetable gardens, and can be sold to home gardeners as compost or fertilizer. Compared to Class B Biosolids, [25]Class A Biosolids are virtually the same, but with stricter limits on pathogens and "vector attraction" (i.e. class A biosolids must not attract disease-carrying insects or rodents, etc). The EPA claims that Class A biosolids must "contain no detectible levels of pathogens" but the only pathogens actually measured and regulated in the law are fecal coliform and salmonella.[38] Despite the U.S. EPA's assurances of safety,[3], the safety requirements for Class A Biosolids do nothing to regulate or limit the numerous other contaminants routinely found in sewage sludge. 1.4 B. Class B bio-solids Class B Biosolids is a designation for treated sewage sludge that meets U.S. EPA guidelines for land application as fertilizer with some restrictions. Compared to Class A Biosolids, Class B Biosolids are allowed to have detectable pathogens. All other regulations for contaminants in the two classes are the same. Despite the U.S. EPA's assurances of safety,[1], the safety requirements for Class B Biosolids are insufficient to ensure safety. Animals fed forage crops grown in soil fertilized with Class B Biosolids have died and humans working in the fields where Class B Biosolids were applied have been sickened. 1.4. C. Class C bio-solids Industrial sludge and waste water sediments are considered as class C bio solids, this types of solids are generated from treatment of effluent by subsequent processes such as oxidation, flocculation, sedimentation etc. this type of sludge are consists of heavy metals, and ions with phosphorus and nitrogen and processing chemicals. The sludge in the effluent treatment plants is currently stored in the treatment unit premises. It creates leachate with toxic metals and organic impurities and cause pollution of ground water and land. It is very essential to manage the sludge generated from the treatment. to be continued….


June 2014
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