Treatment of landfill leachate – high tech or low tech? A case study

At the sanitary landfill of the city of Penzberg (Germany), two diverse approaches to leachate treatment were studied as parts of a three-stage treatment concept. The performance of a simple aerobic pond was compared to that of an advanced multistage treatment unit, the latter comprising a membrane biological reactor and a two-stage activated carbon filter. For 274 days of the year (75%) the pond was able to provide sufficient treatment even under cold weather conditions. For temperatures lower than 5°C, a higher biomass content and temporal storage of the raw leachate (e.g. increasing hydraulic retention time) could close the gap of insufficient treatment. In contrast, the advanced treatment system could only accomplish limited treatment capabilities due to insufficient maintenance, low loading conditions and deficient coordination between the individual treatment steps. As a result, degradation rates were low and operational problems frequent. Limits for Ntot were exceeded regularly (Ntot,e = 60-70 mg/L), throughput broke down and excessive nitrite production occurred (NO2-Ne = 10 mg/L) as a result of microbial activity inside the activated carbon filters. This case study clearly suggests aerobic ponds as an appropriate solution for the treatment of landfill leachate in areas where operational independence is essential

Aerobic granular sludge in an SBR-system treating wastewater rich in particulate matter

Aerobic granular sludge was successfully cultivated in a lab-scale SBR-system treating malting wastewater with a high content of particulate organic matter (0.9 gTSS/L). At an organic loading rate (CODtotal) of 3.4 kg/(m3.d) an average removal efficiency of 50% in CODtotal and 80% in CODdissolved was achieved. Fractionation of the COD by means of particle size showed that particles with a diameter less than 25-50 mm could be removed at 80% efficiency, whereas particles bigger than 50 mm were only removed at 40% efficiency. Tracer experiments revealed a dense sessile protozoa population covering the granules. The protozoa appeared to be responsible for primary particle uptake from the wastewater

Treatment of malting wastewater in a granular sludge sequencing batch reactor (SBR)

Aerobic granular sludge was successfully cultivated in a sequencing batch reactor (SBR) treating wastewater from the malting process with a high content of particulate organic matter. At an organic loading rate of 3.2 kg/(m3 d) CODtotal and an influent particle concentration of 0.95 g/L MLSS an average removal of 50% in CODtotal and 80% in CODdissolved could be achieved. A comparison of granular and flocculent sludge grown under the same operating conditions showed no significant difference in removal efficiency although granules exhibited a higher metabolic activity in terms of specific oxygen uptake rate (rO2, X). Two distinct mechanisms of particle removal were observed for granular sludge: during initial granule formation, particles were incorporated into the biofilm matrix. For mature granules, a high level of protozoa growth on the granule surface accounted for the ability to remove particulate COD. Combined evaluation of the development in MLSS content and sludge bed settling rate (i.e., mean derivative of the normalized sludge volume) was found to be an adequate method for monitoring the characteristic settling properties of a granulizing sludge bed. By means of this method, a distinct substrate gradient out of several operating conditions was concluded to have the biggest impact on the formation of aerobic granular sludge

Drag coefficient of porous and permeable microbial granules

Settling velocity of microbial aggregates, such as anaerobic and aerobic granules, in biological wastewater treatment systems is highly related to their drag coefficient. In this work a new approach, taking the porosity and the permeability into account, was established to evaluate the drag coefficient of porous and permeable microbial granules. The effectiveness of this approach was demonstrated by the experimental results with both the anaerobic and the aerobic granules. The drag coefficient of the microbial granules was found to be less than that of smooth rigid spheres and Biofilm-covered particles. In addition, this study demonstrates that the drag coefficient of microbial granules depended heavily on their permeability and porosity. A fractal-cluster model was found to be able to predict the distribution of the primary particles in the microbial granules