A kinetic study of a membrane anaerobic reactor (MAR) for treatment of sewage sludge

The application of kinetic models (Monod, Contois and Chen & Hashimoto) and overall microbial kinetic on the membrane anaerobic reactor (MAR) for treatment of sewage sludge was investigated. The system consists of a cross-flow ultrafiltration membrane and six steady states were attained over a range of mixed liquor suspended solids of 12,760-21,800 mg/l. The results of all six steady states were successfully fitted above 98% for three known kinetics. The growth yield coefficient, Y, was found to be 0.74 gVSS/gCOD while the specific microorganism decay rate was 0.20 d-1. The k values were in the range of 0.350-0.519 gCOD/gVSS.d and μmax values were between 0.259 and 0.384 d-1. The COD removal efficiency was 96.5-99% with HRT of 7.8 days. The methane gas yield was between 0.19 l/g COD/d to 0.54 l/g COD/d when the organic loading rate increased from 0.1 kg COD/m3/d to 10 kg COD/m3/d. The system efficiency was greatly influenced by SRT and OLRs. Membrane flux rate deterioration was observed from 62.1 l/m2/h to 6.9 l/m2/h due to membrane fouling

Biodegradation of oily wastes and sludges

Improper disposal of petroleum hydrocarbons can cause hazardous effects to both the environment and life. Used and unused oils from several sources contribute to the problems of oil contamination in the environment. Physico-chemical treatment methods are not completely effective as the emission of secondary wastes such as wastes gases and sludges are in the concern. Biodegradation which utilizing microorganisms is therefore an environmentally sound alternative. A case study on microbial isolation and screening of various oily contaminated samples showed that Pseudomonas sp. and Vibrio sp. were present in all oil samples. It was found that the degradation rates depend on incubation temperature

Audit quality, auditor behaviour and the psychological contract

The quality of the opinion provided by audit firms is an important determinant of their long-term survival. However, audit quality is difficult to gauge, which makes it particularly sensitive to the behaviour of the individuals who carry on audit work. Differences of interest between partners and other firm members can then have adverse consequences on the work motivation of field auditors. In particular, audit quality reduction behaviours are defined as actions taken by an auditor during an engagement that reduce evidence-gathering effectiveness inappropriately. These acts can threaten audit quality or damage the reputation of the profession. This paper, which is based on a survey of 170 audit seniors working in large audit firms in France, uses a model based on 'psychological contract' assessment and affective commitment to account for audit quality reduction behaviours by the respondents. The results show that the psychological contract elements dealing with the professional aspect of auditing are the most influential, and that affective commitment is correlated to social but not to technical quality reduction behaviours. The perception, by the respondents, of the quality of the review process is also significant. Some implications of these results for the future of auditing are drawn.