Anaerobic digestion application in the treatment of gelatin-manufacturing effluent

[摘要] ENGLISH ABSTRACT: A severely polluted industrial effluent is generated by the local gelatinmanufacturingindustry. Due to increasingly stringent restrictions on dischargequalities enforced by the National Water Act of 1998 and NationalEnvironmental Management Act of 1998, as well as increasing trade-effluentcharges implemented via the Local Municipal Bylaws, the industry iscompelled to consider a system to pre-treat the polluted effluent.A study was undertaken to examine the viability of anaerobic treatmentof the gelatin-manufacturing effluent, since the anaerobic digestion technologyis well recognised for the high success rate in the treatment of high-strength,complex wastewaters. Various laboratory and pilot-scale studies were done,using different hybrid Upflow Anaerobic Sludge Blanket (UASB) and contactdesigns.Two mesophilic laboratory-scale hybrid UASB digester designs, fittedwith polyethylene (AD-1) and polyurethane (AD-2), performed well at ahydraulic retention time (HRT) of 1.0 d. Chemical oxygen demand (COD)removal efficiencies of up to 90% (avg. 53%) for AD-1 and 83% (avg. 60%) forAD-2 at organic loading rates (OLR) of 9.56 and 4.62 kg COD.m-3.d-1,respectively, were obtained. High sulphate (S04) removal efficiencies of up to96% (avg. 86%) for AD-1 and 98% (avg. 82%) for AD-2 were also achieved,respectively. A maximum total solid (TS) removal of 65% (avg. 25%) for AD-1and 62% (avg. 28%) for AD-2 was reported. An average methane content of80% (AD-1) and 79% (AD-2) with average methane yields per COD removedof 2.19 and 1.86 m3. kg CODremoved.df-o1r AD-1 and AD-2 were found,respectively.When the same digesters (AD-1 and AD-2) were combined in a muItiphaseseries configuration, a total COD removal efficiency of up to 97% (avg.80%) at an OLR of 8.32 kg COD.m-3.d-1,was achieved. Excellent total S04removals of 96% (avg. 69%) were accomplished. Up to 82% TS (avg. 29%)was also removed during this study and the biogas consisted of 89% methane(avg. 79%). For this multi-phase combination up to 92% volatile fatty acids(VFA) (avg. 48%) were removed, indicating possible selective phaseseparation of the respective fatty acid producing/utilising bacterial populations. The use of a laboratory-scale UASB bioreactor with recirculation,resulted in COD removal efficiencies of up to 96% (avg. 51%) at an HRT of 3.0d, and 95% (avg. 54%) at a HRT of 1.0 d. Low performances were generallyfound, with average S04 and TS removals of 59% (max. 97%) and 26% (max.67%), respectively at an HRT of 1.0 d. The biogas production was very lowthroughout the study (0.05 - 0.63 I,d-1).A pilot-scale UASB reactor (300 I) was constructed and performedsatisfactory with a 58% average COD removal and maximum of 96%. S04and TS removals up to 96% (avg. 44%) and 93% (avg. 63%), respectively,were obtained. The methane content of the biogas was 85%. The pilot-scalestudies were conducted under actual field conditions, where various shock andorganic loads had to be absorbed by the system.The pilot-scale contact configuration (300 I) did not perform satisfactoryas a result of continuous blockages experienced in the feed and recirculationlines. Maximum COD, S04, VFA and TS removal efficiencies of 41% (avg.27%), 62% (avg. 41%), 64% (avg. 27%) and 39% (avg. 21%), respectively,were obtained.The results of all the studies indicated acceptable COD removals withincreasing OLR's. Indications of the presence of active methanogenic andsulphate-reducing bacterial populations were apparent throughout the studies.One possibility for the successful start-up and commissioning of the anaerobicreactors was the use of a well-adjusted biomass, which consisted of highlyselected and adapted microbial consortium for the specific gelatinmanufacturingeffluent.It was clear from this study that gelatin-manufacturing effluent can betreated successfully, especially with the use of the UASB design. A welldefineddata base was constructed which could be of great value for furtherupscaling to a full-scale digester.

[发布机构] Stellenbosch University