Follow-up of Nordic projects

However, anaerobic treatment of certain pulp and paper mill waste streams is limited because of the presence of toxic and recalcitrant organic compounds, high concentrations of sulphur and high wastewater temperatures. Sludge from an UASB reactor, sludge from the contact process and a combination of the two types of sludge to different concentrations of the Pulp and Paper Mill Wastewater was exposed with different amendments in methanogenic batch assays (MBA). The characteristics of the wastewater and the results of the MBA demonstrated that it was possible to treat the wastewater in an UASB reactor if sufficient acclimatisation of the sludge and a mixture of the sludges were used. A lab scale UASB reactor was used for treating the wastewater for a period of 300 days with increasing loads of BOD. The results from the period showed that the UASB reactor successfully could be used for this type of wastewater reducing the organic load by 20-40 %. Anaerobic treatment of Pulp Mill Process Water: Spent Sulphite Liquor (SSL), a process stream in a pulp manufacturing plant, containing partially degraded lignosulphonates and hemicellulose is at present utilised for production of ethanol and lignosulphonate derivatives. Ethanol is produced after cellulose removal when the effluent from the pulp mill is subjected to a yeast fermentation utilising the hexoses. The effluent from the fermentation plant contains lignosulphonate- and hemicellulose-residues. The lignosulphonates are a valuable by-product and removal of the hemicellulose residues would be a benefit. Anaerobic treatment for biogas production or fermentation for ethanol production was tested to utilise the hemicellulose residues for yielding products with a potential value. Biogas: Results from batch experiments showed that inhibition of the methanogenic process became more severe for the higher concentrated solutions as seen by longer lag phase and lower rate of production. For the more concentrated samples (50%-100%) there was no production of methane during the experiment. The results from the batch assays showed that the SSL was inhibitory to the methanogenic culture, but also that adaptation to some extent was achieved in the batch cultures. The methane yield was up to 10 L of methane per litre SSL after 60 days of incubation. An UASB reactor was run for 6 months with increasing concentrations of SSL in the feed. When the SSL concentration was increased there were increases in the VFA concentrations indicating instability of the reactor. However, the reactor stabilised as indicated by low concentrations of VFA. The reactor was run at 40% concentration of SSL in the feed with yields between 7 and 17 L of methane per litre of SSL. Ethanol: Initial experiments showed that SSL was toxic to the ethanol-producing bacteria and that adaptation of the organism was needed. Following adaptation the ethanol concentrations in the batch vials were 13 and 25 mM for the 25 and 50% concentrations of SSL, respectively. Growth was not observed in media with higher concentrations of SSL showing that toxicity was present and that further adaptation of the organism will be needed. The growth rate of the microorganism in the diluted media was comparable to the growth rate of the organism in anaerobic medium with xylose (5 g/1) as the carbon source