The results of the action of two glycosidic enzymes added to an anaerobic digester processing mixed wastewater sludge are reported in this paper. The experiment was performed at a continuously operating full-scale wastewater treatment plant during a 6-month period. The addition of the enzyme mixture resulted in improved gas production and dewatering properties. Dewatering experiments, both on enzyme-treated and reference sludge on the local centrifuges, indicated that the carbonaceous matter was decreased by 7% in enzyme-treated sludge, and the average dry solids increased from 27% (reference) to 31% in enzyme-treated sludge. The polymer dosage was decreased from 8 to 5 kg/t dry solids. Additionally, practical experiences were gathered concerning the transformation from static laboratory-scale batch experiments to a dynamic continuous industrial scale setup. Preliminary cost calculations showed beneficial aspects and economical feasibility of enzyme addition to an anaerobic sludge digestion process.
Glucose, enzymatically released from pulp fiber sludge, was combined with inorganic salts and used as a growth medium for Alcaligenes eutrophus, a gram-negative strain producing poly(3-hydroxybutyrate) (PHB). By controlling the concentrations of the inorganic salts in the growth medium, almost 78% of the cell mass was converted to pure PHB. Efforts were made to find conditions for bacterial growth in the form of a biofilm on a cheap and reusable carrier. A number of positively charged carriers were tested, and the anion exchanger DEAE-Sephadex A-25 was chosen as a microcarrier for packed-bed biofilm cultures of A. eutrophus. Conditions for attachment, growth, and detachment were established. Biofilm formation on the microcarrier is strongly dependent on the ionic strength of the attachment medium. In order to achieve formation of the biofilm and its recovery from the microcarrier, the ionic strengths of the attachment and the detachment media were varied. Low ionic strength was tested for attachment, and high ionic strength was tested for detachment. Although biofilm formation in the packed-bed reactor is limited, the volumetric yield of cells based on the void volume of the packed bed is comparable with the batch culture yield.
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