ANAEROBIC 35-DEGREES-C AND 55-DEGREES-C TREATMENT OF A BCTMP TMP EFFLUENT - SULFUR MANAGEMENT STRATEGIES

Pulp manufacture uses sulphur in a variety of forms and these sulphur compounds ultimately end up in the effluent. Under anaerobic condition s, sulphite and sulphate are reduced to sulphide, presenting problems of toxicity, odour, corrosion, and reduced methane yields and treatmen t efficiencies. The fate of these inorganic sulphur compounds in a ble ached chemi-thermomechanical pulp/thermomechanical pulp (BCTMP/TMP) ef fluent mixture was examined in two phase anaerobic reactors at 35-degr ees-C and 55-degrees-C. The following sulphur management strategies we re investigated: 1) controlling the pH of the acidogenic reactor, 2) i nhibiting the sulphur reducing bacteria via molybdenum addition to the feed tank, and 3) stripping the hydrogen sulphide dissolved in the me thane phase reactor liquor by recycling hydrogen sulphide-free off gas . The laboratory scale experimental apparatus consisted of upflow anae robic sludge bed pre-treatment or acidogenic reactors followed by hybr id upflow anaerobic sludge bed/fixed film methanogenic reactors. At 35 -degrees-C, controlling the pH of the acidogenic reactors with sodium carbonate from 5.5 (uncontrolled) to 8.0 in order to shift the formed sulphide species to the less toxic ionic form appeared to be ineffecti ve in promoting wastewater treatment efficiency. Molybdenum addition t o the wastewater at levels from 0.1 to 1.0 mM was effective at 1.0 mM in retarding sulphate reduction or sulphide formation. Hydrogen sulphi de stripping, using ferric chloride scrubbed and recycled off gas, app eared to be the most effective means of sulphur management for this ty pe of wastewater under these conditions. Thermophilic 55-degrees-C ana erobic treatment was also studied using the same effluent, inocula and sulphur management strategies. Overall, both the treatment efficiency and the sulphate reduction were lower for the thermophilic runs compa red to the mesophilic runs. Raising the acidogenic phase reactor pH fr om 7.0 to 7.5 to 8.0 appeared to have no significant effect on organic carbon removal efficiency or on sulphate reduction. Molybdenum inhibi tion of sulphur reduction was not as marked as for the 1.0 mM level at 35-degrees-C, perhaps due to the already low baseline sulphate reduct ion efficiency at 55-degrees-C. Stripping hydrogen sulphide from the r eactor liquor helped to promote the treatment efficiency and lowered t he sulphide and sulphate levels. Similar to the 35-degrees-C study, su lphide removal by gas stripping appeared to be the most effective mean s of sulphur management.