Advanced oxidation of refractory organics in leachate--potential methods and evaluation of biodegradability of the remaining substrate.

An assessment of potential methods suitable for degradation and/or reduction of refractory organics was performed on landfill leachate from SYSAV AB, Malmö, Sweden. Pretreatment of the leachate was performed in a sequence batch reactor designed for nitrification in activated sludge. Oxidation of the leachate was then O3, O3/pH adjustment (pH 9 and 10), H2O2, O3/H2O2 and performic acid in lab-scale reactors. The degradation of organic material was followed with chemical oxygen demand (COD) measurements for all experiments except for the performic acid treatment for which total organic carbon (TOC) measurements were used. The potential degradation of refractory organics into biodegradable organic material was analysed by subsequent oxygen uptake rate (OUR) measurements in laboratory batch reactors. Ozonation of biologically pre-treated leachate increased reduction of the organic material. The most biodegradable organic material was produced after oxidation with only ozone and ozonation at pH 9. Performic acid did not reduce the content of organic material in the leachate. However, a combination of biological pretreatment, chemical oxidation with O3/H2O2 and a subsequent biological process resulted in the most efficient oxidation method for the tested leachate.

Mixed carbon sources for nitrate reduction in activated sludge-identification of bacteria and process activity studies.

Mixtures of methanol and acetate as carbon source were investigated in order to determine their capacity to enhance denitrification and for analysis of the microbial composition and carbon degradation activity in activated sludge from wastewater treatment plants. Laboratory batch reactors at 20 degrees C were used for nitrate uptake rate (NUR) measurements in order to investigate the anoxic activity, while single and mixed carbon substrates were added to activated sludge. Microautoradiography (MAR) in combination with fluorescence in situ hybridisation (FISH) were applied for microbial analysis during exposure to different carbon sources. The NUR increased with additions of a mixture of acetate and methanol compared with additions of a single carbon source. MAR-FISH measurements demonstrated that the probe-defined group of Azoarcus was the main group of bacteria utilising acetate and the only active group utilising methanol under anoxic conditions. The present study indicated an improved denitrification potential by additions of a mixed carbon source compared with commonly used single-carbon additions. It is also established that Azoarcus bacteria are involved in the degradation of both acetate and methanol in the anoxic activated sludge.

Hydrolysis of return sludge for production of easily biodegradable carbon: effect of pre-treatment, sludge age and temperature.

Return sludge from two Swedish and two Danish wastewater treatment plants were hydrolysed in laboratory reactors. Treatment plants with/without pre-sedimentation and with/without nitrification were represented. Soluble organic matter was produced from all types of sludge, but the yield was to a large extent dependent on what type of sludge was hydrolysed. Activated sludge from wastewater treatment plants without pre-treatment returned more soluble carbon after hydrolysis than sludge from treatment plants with pre-sedimentation. In addition, more soluble carbon was formed from non-nitrifying activated sludge than from nitrifying sludge. Moreover, the maximum yield of soluble COD at 10 degrees C was less than the yield at 20 degrees C. The initial hydrolysis rate was found to be between 0.35 and 1.8 mg soluble COD/(g VS x h). With the exception of one case, between 15 and 50% of the produced soluble COD was shown to be volatile fatty acids, a suitable carbon source for biological phosphorus removal. Nitrification rate measurements indicated that the viability of the activated sludge was not affected by the hydrolysis.

Biological detoxification of tar-water.

Gasification is an important option for the swift implementation of biomass combined heat and power processes in the Danish energy supply system. Tar-water produced by the gas-cleaning system of gasifiers may contain substances toxic to nitrifying bacteria. As the gasification plants are small and often located in the catchment area of small wastewater treatment plants, discharge of the tar-water may be critical for wastewater treatment plants operated with nitrogen removal. Tar-water from a full-scale updraft gasifier has been thoroughly examined with respect to inhibition of nitrification and the toxicity for nitrifying bacteria has been evaluated for the dominating constituents in the tar-water. Simple organic substances make up the dominating part of the organic matter but phenol and phenolic compounds are also present in significant concentrations. The identified substances are biologically degradable and it has been demonstrated that most of the organic matter together with the toxicity can be eliminated in an aerobic activated sludge process.

Use of phosphorus release batch tests for modelling an EBPR pilot plant.

The aim of this study was to evaluate how routinely performed phosphorus release tests could be used when modelling enhanced biological phosphorus removal (EBPR) using activated sludge models such as ASM2d. A pilot plant with an extensive analysis programme was used as basis for the simulations. Without any calibration the prediction of phosphorus removal was poor and the initial release rates from the simulations were not similar to those found from the laboratory tests. A period with low organic loading was chosen as a calibration period. In this period averages of daily influent measurements were used as influent parameters. First, calibration was performed in order to fit effluent COD and MLVSS in the sludge. Next, the phosphorus content in the sludge was decreased to the measured level by decreasing the fermentation rate. Finally, the initial phosphorus release rate was calculated from a simulated batch test and the PHA uptake rate was increased to fit this release rate with the average initial rates from laboratory batch tests performed during the period. The calibrated model was verified with data from the subsequent period where acetate was dosed.