Increasing legislation and rising treatment and disposal costs have promoted optimisation of the activated sludge process to encompass reduction of waste biomass. Manipulation of process control such as increasing sludge age and decreasing food to microorganism ratio can lower waste sludge production, but capital works as well as increased operating costs in the form of power requirement for oxygen supply may be required. The need for a cost effective method of biomass reduction without capital expenditure has prompted research into methods beyond process control. The use of chemicals capable of disrupting microorganism metabolic pathways can theoretically allow continuation of catabolic (degradative) paths whilst halting some or all of the anabolic (growth) pathways. This project explored the use of metabolic inhibitors (uncouplers, tricarboxylic acid cycle inhibitors and antibiotics) to reduce the yield of the activated sludge process. Initial respirometric studies identified many chemicals capable of interacting with the activated sludge microorganisms. Increased oxygen uptake rate was taken as an indication of a good uncoupler, and tests highlighted 4 chemicals with significant potential for achieving biomass reduction (trypan blue, rotenone, 2,4 DNP and 4 NP). These chemicals were then tested at a laboratory scale and at bench scale in both batch and continuous simulations. Simulations were carried out using activated sludge and settled sewage feed to obtain as realistic conditions as possible. In batch tests, trypan blue, rotenone and 2,4 DNP successfully reduced mixed liquor suspended solids accumulation with little effect on COD removal compared to controls. In continuous simulations, 2,4 DNP and 4 NP both lowered yield with respect to their relative controls. Rotenone addition did not result in lowered yield. In all cases, any yield reduction was not at the expense of process efficiency in terms of COD and BOD removal. At pilot scale, 2,4 DNP almost halved the observed yield compared to the control whilst having no significant effect on BOD, COD or ammonia removal, nitrite and nitrate production, SVI or CST. Addition of chemical uncouplers had little effect on the species diversity of the activated sludge though a reduction in the floc size was observed in treated samples. Selection of a suitable chemical can result in reduced yield without detrimental effect to process efficiency in the activated sludge process. An increase in oxygen consumption occurred which has an associated cost implication, but this was not found to be significant compared to the savings made by reducing the yield.

No description available.

The rate at which volatile organic compounds (VOCs) are removed from the vadose zone by forced ventilation may be reduced by slow micro-scale processes such as diffusion through intra-aggregate and pore water and slow reactions at sorption sites located at the soil-water interface. Column experiments using benzene and p-xylene were performed in order to simulate cleanup of VOC's in the vadose zone by forced ventilation. Analytical solutions of the one-dimensional advection-dispersion equation coupled to mass transfer equations were fitted to the data. Parameter estimates were used in order to determine time scales of diffusion through water, desorption from, and sorption to, soil organic matter. Lower limits for the time scales for these processes were calculated to be on the order of minutes. Results indicate that these micro-scale processes reduce the rate of removal on the laboratory scale but may have no effect on the field scale.

No description available.

No description available.

No description available.

Data for ten chemical parameters, obtained from the routine chemical monitoring programme for 49 sites in the Foyle River catchment, were assessed for temporal trends. Results suggest: A downward trend in dissolved oxygen concentration (%DO) at a majority of sites; An indication of a widespread upward trend in nitrate concentration; Evidence that increases in nitrate concentration occur a sites after rainfall following dry periods; No corresponding upward trend in Biochemical Oxygen Demand (BOD); Eutrophication as the main water-quality problem in the Foyle River catchment. Biological and chemical General Quality Assessment of the Foyle River sites classifies only 7 sites to the same classification band. Ordination of 10 sites was carried out using the seasonal averages of BOD, %DO, and NH4-N for each site and repeated using Spring, Summer and Autumn macroinvertebrate abundance data. Spearman Rank correlation suggests that BOD, %DO, and NH4-N have little influence in structuring the community composition at the sites. Comparison of species and family-level ordinations appears to support family-level identification in a monitoring programme although species of the same family show different correlations to the determinants. Family-based scoring may not reflect the complexes of species level responses to these variables. Multivariate analysis indicates that some pollution-sensitive species are correlated with greater than average BOD concentration. The removal of such species results in an increase of 3.1% in the % variance in the Spring data explained by the three variables, while Autumn is unchanged. The variance of the species-based data and the family-based ‘explained’ by the three variables in each season is essentially unchanged. Recalculation of Ecological Quality Indices (EQIs) for the 10 sites after these species are removed indicates that the number of sites classified to the same band is increased.

No description available.

No description available.

No description available.