F. Tran

Heavy metals removal from anaerobically digested sludge by chemical and microbiological methods

The metal removal from anaerobically digested sludge was studied by chemical treatment and microbial leaching processes in laboratory reactors. The removal of metals increased with decreased sludge solid concentration and pH. In the acid treatment process, a pH of 1.5 was required to reduce the copper concentration in the sludge to an acceptable level. In the microbial processes mixed culture gave 10% better solubilisation of metals than in single culture. The acid requirement was lower for the microbial process. The cost of sludge treatment in terms of chemicals was found to be decreased by 80% in microbial leaching.

Slaughterhouse effluent treatment by thermophilic aerobic process

A pig slaughterhouse effluent was submitted to laboratory runs in order to assess the potentiality of the thermophilic aerobic process for the treatment of meat processing industrys effluents. A mixed aerobic bacterial culture was successfully maintained at 52 and 58°C in a semi-continuously fed bioreactor, without recycling the cells. Operation was conducted at 6, 12, 18, 24 and 30 h of solids retention time. Over 93% of the CODs (Chemical Oxygen Demand) were removed during the treatment at 52°C for all the retention times investigated, as compared to 86% of removal at 58°C, with an exception for the case of 6 h retention time. Reduction of phosphorus in the form of orthophosphate ranged between 72–90% with the best efficiency noted at 52°C and 6 h retention time. Extremely high specific utilization rates (qm) were observed and revealed that the process is about 10 times faster than the mesophilic process for slaughterhouse effluent treatment. Biokinetics parameters μm (maximal specific growth rate) and kd (endogenous respiration coefficient) were evaluated by fitting to appropriate mathematical models. They were found superior to those reported in the literature for mesophilic process, with the exception of the Y (actual yield) coefficient which is of the same magnitude. High kd values had a marked effect on the apparent yield of sludges which showed low values as compared to those found in mesophilic systems.

Comparative study of bacterial leaching of metals from sewage sludge in continuous stirred tank and air-lift reactors

Abstract A comparative study between continuous stirred tank reactor (CSTR) with cell recycle and air-lift reactor was carried out in 30 l capacity reactors for metal solubilization from anaerobically digested sludge. In CSTR at a residence time of 0·75 day, supplementing the feed sludge with 4 g/l of FeSO 4 ·7H 2 O, using 20% sludge recycle and adjusting the pH of the feed sludge to 4·5 resulted in the following metal solubilization: 91% Cu, 94% Zn, 93% Mn, 67% Cd, 67% Ni, 8% Cr, and 7% Pb. At a retention time of 0.75 day, metals were solubilized to the recommended level in the CSTR as well as in the airlift reactor. The treated sludge was easy to filter in a plate filter press, by centrifugation, or by vacuum filter. The sludge nutrients did not seem to be diminished as a result of treatment and separation of the solid from the liquid. The ammonia-nitrogen fraction seems to be transformed to organic nitrogen. The decontaminated sludge produced has reduced odour.

Thermophilic process for protein recovery as an alternative to slaughterhouse wastewater treatment

Abstract Thermophilic aerobic treatment of slaughterhouse waste was carried out in a laboratory bioreactor at different temperatures and solids retention times without cell recycle. COD was reduced by over 93%. Phosphorus was removed from 72 to 90% under different cultivation conditions. A high rate of specific substrate consumption was observed compared to that obtained in mesophilic processes. The biokinetic constants were evaluated. Crude protein content of the biomass varied from 64 to 78%. The composition of the essential amino acids in the biomass was similar to that of meat and soya meals and appeared well-balanced and appropriate for pigs and poultry feeding.