Molecular weight distribution of Pinus radiata kraft mill wastewater treated by anaerobic digestion

Kraft mill is responsible for massive discharge of highly polluted effluent s. The main characteristics of this effluent are high toxicity and low biod egradability due to tannin, lignin and chlorophenol compounds. The composit ion may vary dramatically depending, for instance, on the utilised feedstoc k and process. The purpose of this work was to investigate the molecular we ight distribution of Pinus radiata kraft pulping wastewater treated by anae robic digestion by using two types of anaerobic reactors: fixed bed and slu dge blanket. Anaerobic sludge blanket (UASB) and anaerobic filter (AF) were operated. In both reactors, the total alkalinity ranged between 1.0 and 1.5 g CaCO3/l, while the organic load rate (OLR) was increasing during operation from 1.2 to 3.3 gCOD/l d. COD and total phenolic compounds (UV215) removal ranged be tween 30-50% and 13-20%, respectively, while the BOD5 removal ranged 60-90% . However only a partial biodegradation (10-43%) of tannin and lignin was o bserved. Results from ultrafiltration analyses indicated that the fraction with a molecular weight (MW) <1000, COD and colour decreased after anaerobi c treatment, but the total phenolic compounds increased. In the 1000 < MW < 10,000 fraction, there was no change in COD, UV215 and colour. In the >10, 000 MW fraction, colour and COD fraction increased by 14% and 5%, respectiv ely, after anaerobic treatment. It can be concluded from this study, that t reatment with UASB or AF reactors is not enough, under the conditions teste d, for a large COD removal from Pinus radiata wastewater. (C) 2001 Publishe d by Elsevier Science Ltd.