Analysis of forced convective evaporation system for tannery effluent (soak liquor)
01 Jul 2003-International Communications in Heat and Mass Transfer (Pergamon)-Vol. 30, Iss: 5, pp 727-736
TL;DR: In this paper, the authors proposed a forced convective evaporation system for tannery effluent (soak liquor), which facilitates direct contact heat and mass transfer between liquor and air.
About: This article is published in International Communications in Heat and Mass Transfer.The article was published on 2003-07-01. It has received 3 citations till now. The article focuses on the topics: Evaporation & Mass transfer.
Citations
More filters
TL;DR: In this paper, a batch recirculation cell was used to treat the soak liquor, tanning effluent, and post-tanning wastewater for electrochemical treatment, which achieved a significant reduction in the chemical oxygen demand (COD, 94.8%) under conditions of a circulation flow of 142.8 L h -1, a current density of 5.8 A dm -2, and a time of 7.05 h.
Abstract: The performance of conventional biological treatment of tannery wastewater can be improved by the application of electrochemical treatment to selected streams. In this study, soak liquor, tanning effluent, and post-tanning effluent were electrochemically treated in batch recirculation mode. The experiments were designed, modeled, and optimized using response surface methodology. Considerable removal of chemical oxygen demand (COD, 94.8%) was achieved by treating the soak liquor in a batch recirculation cell under conditions of a circulation flow of 142.8 L h -1 , a current density of 5.8 A dm -2 , and a time of 7.05 h. Salt remaining in the treated soak liquor was partly utilized in improving the ionic conductivity of the post-tanning effluent for electrochemical treatment. In a separate treatment, the biodegradability index of the post-tanning effluent was improved from 0.3 to 0.67 under conditions of a circulation flow of 112.5 L h -1 , a current density of 2.4 A dm -2 , and a time of 2.15 h. Considerable reduction in the requirement of reactor volume or residence time of the existing aerated biological treatment system of the total wastewater stream can be achieved by applying such an electrochemical pretreatment. 1. Introduction The leather industry encompasses more than 5000 tanneries partly scattered all over the region of South Asia. Most of the tanneries are of small scale, processing 2-3 tons of hides or skins per day. Approximately 30-40 m 3 of wastewater is produced for every ton of hide or skin processed. The total production capacity of the region covers 20% of the world market share. This invites special attention to environmental issues related to the wastewater generated in tanneries. Wastewater from tanneries usually contains high concentrations of chlorides, aliphatic sulfonates, sulfates, aromatic and aliphatic ethoxylates, sulfonated polyphenols, acrylic acid condensates, fatty acids, dyes, proteins, soluble carbohydrates, and Na2S. These substances are either derived from hides and skins or obtained upon addition of reagents during the process. The characteristics of tannery wastewater vary depending on the nature of the tanning process adopted, the amount of water used, the process of hide preservation, the hide processing capacity, and the in-plant measures followed. 1 Raw skins and hides are received in tanneries in salted condition; nearly 40% sodium chloride salt by weight is used in preserving the skins. The first processing step is to wash them with water to remove the salt and other particles. After this washing, a large quantity of water is released as wastewater. This stream, called soak liquor, consists of 2-4% sodium chloride by weight and contains traces of calcium chloride along with bioparticles such as blood, flesh, skin, and other suspended particles. The dissolved salts, especially chlorides, are a matter of concern when the effluent is discharged into nearby lands or stored in ponds. In the long run, it makes fertile land barren, in addition to polluting the surrounding groundwater. Therefore, it becomes necessary to tackle the problem on a priority basis to control the severe environmental degradation caused by soak liquor. The most common method of disposing of soak liquor is evaporation in shallow solar ponds. The soak liquor is sent to shallow solar ponds, and the water in these ponds is removed through a natural evaporation process. The operation is slow and season-dependent. Research is ongoing to improve equipment to enhance the rate of heat transfer and thus the evaporation rate, 2,3 as well as to develop alternate techniques such as membrane processes. 4 The match of electrochemical treatment with tannery soaking effluent is due to multiple reasons: the presence of a high concentration of NaCl, the most effective supporting electrolyte; the moderately lesser quantity to handle (6-10 m 3 per ton of skin), and the failure of conventional methods. The wastewater from small-scale tanneries is usually managed by treatment in common effluent treatment plants (CETPs) for a cluster of tanneries. Most of the large- and medium-scale tanneries have their own effluent treatment plants (ETPs). The CETP process includes the primary treatment (coagulation followed by clarification) and the biological treatment where the dissolved organic part is also removed. The capacity of microorganisms to degrade some groups of tannins is limited by a conventional biological process in either aerobic or anaerobic environments. 5,6 Moreover, variations in pH values, effluent composition, contaminant type, structure, and concentration can inhibit the functioning of an established biological system, thus paralyzing the microorganism metabolism. Other limitations of biological process include the long time needed for the effluent to reach the required standards and the low color removal efficiency. Tannery wastewater treatment by biological processes can still be difficult because of the presence of broad spectrum biocides used in the leather industry to prevent fungal
31 citations
TL;DR: In this paper, a non-linear regression analysis has been carried out using these experimental data and the empirical correlations are presented for various salt concentrations of soak liquor ranging from 3% to 20%.
9 citations
TL;DR: In this article, a numerical technique for evaluating the performance of forced convective evaporation system for tannery effluent is presented, which treats the airflow to be two dimensional and liquid flow to be one-dimensional.
5 citations