The objective of this study was to investigate the anaerobic biological treatment of an organic-bearing wastewater from a particular paper manufacturing process at laboratory scale. The process produces paper by re-pulping waste paper. Effluent from the process has a Chemical Oxygen Demand CCOD> concentration of approximately 4500 mg/l with a sulphate content of approximately 300 mg SQ4 2 -/l. The upflow anaerobic sludge bed CUASB> reactor was selected for the study. Important information derived from the laboratory treatability study was: Cl> the extent of COD removal possible! (2) the effluent quality! <3> the maximum COD leading rate CkgCOD/m3 reactor/day) which can be achieved while maintaining reasonable COD removal. and the influence on loading rate of temperature: (4) the nature of the sludge produced in the reactor with particular reference to the extent of pelletisation: and (5) the effect of reactor effluent recycling on alkalinity requirements. The following specific conclusions may be itemised from the results obtained: Wastewater characteristics and chemical addition: (1) The waste is amenable to anaerobic treatment in a UASB system. <2> The unbiodegradable COD content of the waste is in the region of 10 to 15 percent, and COD removals of approximately 85 percent are possible on a continuous basis. <3> The short chain volatile fatty acids acetic and propionic comprise approximately 45'percent of the COD in the influent. The remainder is made up principally of starch, carbohydrates and more complex organics. (4) The wastewater is deficient in the elements nitrogen and phosphorus. These elements must be supplemented through chemical addition in order to achieve complete anaerobic treatment. (5) The wastewater is acidic, with a pH in the range 5 to 6 generally. Alkalinity must be added to the waste prior to treatment to adjust the pH to approximately neutral. Organic loading rates: (6) Organic loading rates of approximately 25 kgCOD/m3 reactor/day were attained at both 25 and 35°C. This corresponded to a hydraulic retention time of 5 hours at an influent COO concentration of 4500 mg/1. The loading rate was not constrained by limitations in the biological treatment capacity. Rather, difficulties associated with the settleability of the sludge were encountered: blockages of the under-designed laboratory reactor settler occurred. Sludge characteristics: (7) A dense bed of biological sludge extended from the base to approximately half the height of the UASB reactors. This sludge had a granular, well-flocculated form with the floes appearing to be in the size range 1-2 mm. Very fine sludge was also present within the bed. A small number of true sludge pellets <4-5 mm) were present within the dense sludge bed1 particularly near the base. <B> The settleability of the dense granular sludge appeared reasonable, and the bed was not disturbed unduly by gas production. However.the settleability of the sludge was inferior to that of a wellpelletised sludge. (9) The absence of true sludge pellet formation appears to relate to the absence of a high hydrogen partial pressure zone in the lower region of the UASB ·reactor. With this particular wastewater two factors appear to reduce the possibility of creating a high partial pressure of hydrogen near the inlet, thus reducing the possibility of pellet formation. These are Cl> the nature of the feed, and <2> the role of sulphate reduction. Nature of feed: Approximately 45 percent of the influent COD is in the form of acetic and propionic acid. Therefore, the amount of remaining substrate available for acidogenesis1 with its associated

show more