Browsing by Issue Date, starting with "2009-08-08"
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- Combined biologic removal of sulphate for tanning industrial wastewatersPublication . Di Berardino, SantinoA biologic pretreatment technology of mixed tanneries wastewater, suitable for sulphate-rich industrial wastewaters, has been studied, in order to eliminate chemical precipitation and improve removal efficiency of the relevant pollutants. It couples an anaerobic reactor with an aerobic sulphide oxidant (ASO) step, where H2S2 is partially oxidized to elemental sulphur, and includes a recirculation system. The proposed solution provided Methanogenic Archae (MA) and Sulphate Reducing Bacteria (SRB) coexistence and controlled inhibition by partial oxidation of hydrogen sulphide.. The removal effiency of the anaerobic reactor was quite dependent on temperature and hydaulic retention time (HRT). COD removal varied between 32-68 % and sulphate removal (20-60%), referred to the mixture of the industrial effluent diluted with 50% of recirculation, at an Organic Load (OL) ranging from 0.5 to 1.5 kg CODM³ d⁻¹ and HRT from 1 to 5 days. The entire biologic pretreatment (AHF+ASO) resulted much more efficient and COD removal increased to 64-82% being less dependent on temperature variations. This process removed also a significant part (85%) of Chromium (Cr⁺³), by sorption into the biologic sludge. This two step biologic pretreatment, ensured better removal of relevant parameters than conventional chemical precipitation, avoided addition of chemical products, minimized excess sludge production, and also removed hydrogen sukphide and sulphate, resulting in a favorable alternative solution. The effluent from this stage was submitted to a sequencing batch nitrification/denitrification step, to improve the removal of the relevenat parameters. The average removal efficiency of entire process was appreciable and better than the conventional solution: COD = 88%, Sulphate = 68% and Nitrogen (kjeldahl) = 92%, chromium (Cr⁺³=96%). However, the presence of non degradable organic compounds delivered in the effluent from syntetic tanning, were hard to remove completely and did not allow fulfilling the severe standards for wastewater discharge in water course in terms of COD, Nitrogen (kjeldahl) and color. This requires and additional polishing step
- Co-digestion of tanning residues and sludgePublication . Di Berardino, Santino; Martinho, AlcinoCodigestion experiments on sludge from tanneries’ industrial wastewater treatment plant (WWTP) mixed with chromium free (“green”) tanneries solid wastes were carried-out in a 15 m3 pilot plant reactor, operating at 20 days hydraulic retention time (HRT) and at mesophilic temperature (35 ºC). The goal was to evaluate the feasibility of a full-scale unit. Addition of “green” solid wastes improved biodegradability of the sludge and biogas production. The removal efficiencies of organic matter varied, according to the feedstock mixture. Averaged results are: COD and VS more than 55 %; TOC = 69 %. Hydrolysis of suspended volatile solids was initially moderate (36 %), but increased up to about 50 %, when the feedstock contained proteolytic enzymes. Fat removal was quite high (77 %). Biogas production was highly dependent from the fleshing content in the feedstock. Addition of 30 % by weight of fleshing to the sludge increased 4 times the average biogas production (from 3,85 m3/day to 14,62 m3/day). The maximum Biogas production rate was 38 liter/kg of feedstock. Fleshing biogas yield was found to be 630 l/kg Volatile Solids loaded, higher than the value recorded for the sludge (288 l/kg Volatile Solids loaded). Methane content in biogas was about 75 % CH4. The average biogas productivity of the reactor was 1.49 l/l/day. Sulphate removal carried-out by the biologic community (SO4 = ≥ 35%) increased Hydrogen sulphide concentration in the biogas up to 1800 ppm (average), a value higher than the limits allowed for use in internal combustion engines. Grinding and maceration of fleshing was hard, due to smell, repugnant look and high strength of its components. This feedstock must be pre-treated in order to avoid excess hydrogen sulphide and lime. Codigestion of “green” tannery wastes with sludge and others residues revealed technically feasible and a low cost solution for the environmental problem of these residues from small/average tanning factories. The potential biogas production for full scale plant is about 11 000 m3/day, making this solution refundable within 5 years. Codigestion allows substantial reduction in bio solids volume, pathogens, and odor, increasing landfill life. This is an important evolution on current solution and gives time to plan and implement new sustainable projects.