Organic matter parameters in WWTP - a critical review and recommendations for application in activated sludge modelling.

This paper includes a comprehensive literature review of sludge composition data from wastewater treatment plants. 722 data sets from 249 sources were used to establish typical ratios between COD and solids-based parameters and to verify rule-of-thumb values, respectively. Confirmation of these typical ratios can also be accomplished by using biochemical composition data. It is shown that a correlation between data from proteins, lipids and carbohydrates analysis can be related to COD/VSS ratios. Finally, using the findings from the literature review, the organic and inorganic conversion factors of COD fractions in activated sludge models are adjusted to solids-based parameters. It was shown that with the adjustments of the factors and a partition of the particulate inert fraction into a fraction assigned to the influent and a fraction assigned to the endogenous products, a better agreement with the ratios of COD/VSS in the individual sludge streams can be established.

Growth of science in activated sludge modelling - a critical bibliometric review.

In this paper, the tool of bibliometric analysis is applied to the field of activated sludge modelling and its suitability as a first step of a literature analysis is assessed. The analysis is applied to the total dataset considered as well as a time-based classification. It can be shown that this tool is very well suited to filtering the relevant authors and publications, thus enabling a subsequent visual review. The methodology presented can also be applied to sub-disciplines or other subject areas. However, the sole use of the multiple statistical and visual tools is critically questioned. Thus, misinterpretations and apparent findings can result from structural problems in the data or parameters used. Not all of the metrics used are suitable for finding relevant publications, but rather for ranking the criteria studied. However, the latter represents the most widespread application of bibliometrics. From the analysis of the keywords, it could be deduced that there has been a temporal shift from fundamental model aspects to detailed questions such as the integration of sorption and adsorption processes or anaerobic digestion. The modelling of biological phosphorus removal has also surprisingly lost a great amount of importance in the scientific literature.

Operational experience with a full-scale anaerobic baffled reactor treating municipal wastewater.

The aim of the study was to investigate the influence of moderate temperatures on the efficiency of a full-scale anaerobic treatment system consisting of a primary sedimentation unit (PST) and an anaerobic baffled reactor (ABR, approx. 10 m3 ). Therefore, two trials with different test setups in series were carried out (1st trial: continuous load; 2nd trial: diurnal variation load). The plant was fed with municipal wastewater and operated at temperatures between 8 and 24°C. The mean efficiency of the ABR was low, compared to the one of the PST. At 10°C, only 10% of the COD was removed. The COD (chemical oxygen demand) removal efficiency of the plant (PST + ABR) averaged 50%. At low temperatures, volatile fatty acids began to accumulate. In both trials, the contents of total suspended solids in the sludge bed differed distinctly and influenced the effort for desludging. PRACTITIONER POINTS: The operation of ABR in combined collection systems depends on the efficiency of the pretreatment unit. At cold temperatures, an ABR has no advantages compared to conventional pretreatment processes. For use under moderate conditions, the design must be adjusted.

A black-box model for generation of site-specific WWTP influent quality data based on plant routine data.

This paper presents a simple method for the generation of continuous influent quality datasets for wastewater treatment plants (WWTPs) that is based on incomplete available routine data, only, without referring to any further measurement. In the approach, Weibull-distributed random data are fitted to the available routine data, such that the resulting distribution of influent quality data shows the identical statistical characteristics. Beside the description of the method, this paper contains a comprehensive analysis of robustness and universality of the approach. It is shown that incomplete datasets with only 10% remaining influent quality data can be filled with this method with nearly the same statistical parameters as the original data. In addition, the use with datasets of different WWTP plants sizes results always in a good agreement between original and filled datasets.

Mass flow of antibiotics in a wastewater treatment plant focusing on removal variations due to operational parameters.

Wastewater treatment plants (WWTPs) are not designed to purposefully eliminate antibiotics and therefore many previous investigations have been carried out to assess their fate in biological wastewater treatment processes. In order to consolidate previous findings regarding influencing factors like the solid and hydraulic retention time an intensive monitoring was carried out in a municipal WWTP in Germany. Over a period of 12months daily samples were taken from the in- and effluent as well as diverse sludge streams. The 14 selected antibiotics and one metabolite cover the following classes: cephalosporins, diaminopyrimidines, fluoroquinolones, lincosamide, macrolides, penicillins, sulfonamides and tetracyclines. Out of the 15 investigated substances, the removal of only clindamycin and ciprofloxacin show significant correlations to SRT, temperature, HRT and nitrogen removal. The dependency of clindamycin's removal could be related to the significant negative removal (i.e. production) of clindamycin in the treatment process and was corrected using the human metabolite clindamycin-sulfoxide. The average elimination was adjusted from -225% to 3% which suggests that clindamycin can be considered as an inert substance during the wastewater treatment process. Based on the presented data, the mass flow analysis revealed that macrolides, clindamycin/clindamycin-sulfoxide and trimethoprim were mainly released with the effluent, while penicillins, cephalosporins as well as sulfamethoxazole were partly degraded in the studied WWTP. Furthermore, levofloxacin and ciprofloxacin are the only antibiotics under investigation with a significant mass fraction bound to primary, excess and digested sludge. Nevertheless, the sludge concentrations are highly inconsistent which leads to questionable results. It remains unclear whether the inconsistencies are due to insufficiencies in sampling and/or analytical determination or if the fluctuations can be considered reasonable for digesters. Hence, future investigations have to address antibiotic's temporal dynamics during the sludge treatment to decide whether or not the widely reported standard deviations of sludge concentrations reflect realistic fluctuations.

Representative input load of antibiotics to WWTPs: Predictive accuracy and determination of a required sampling quantity.

Predicting the input loads of antibiotics to wastewater treatment plants (WWTP) using certain input data (e.g. prescriptions) is a reasonable method if no analytical data is available. Besides the spatiotemporal uncertainties of the projection itself, only a few studies exist to confirm the suitability of required excretion data from literature. Prescription data with a comparatively high resolution and a sampling campaign covering 15 months were used to answer the question of applicability of the prediction approach. As a result, macrolides, sulfamethoxazole and trimethoprim were almost fully recovered close to 100% of the expected input loads. Nearly all substances of the beta-lactam family exhibit high elimination rates during the wastewater transport in the sewer system with a low recovery rate at the WWTP. The measured input loads of cefuroxime, ciprofloxacin and levofloxacin fluctuated greatly through the year which was not obvious from relatively constant prescribed amounts. The latter substances are an example that available data are not per se sufficient to monitor the actual release into the environment. Furthermore, the extensive data pool of this study was used to calculate the necessary number of samples to determine a representative annual mean load to the WWTP. For antibiotics with low seasonality and low input scattering a minimum of about 10 samples is required. In the case of antibiotics exhibiting fluctuating input loads 30 to 40 evenly distributed samples are necessary for a representative input determination. As a high level estimate, a minimum number of 20-40 samples per year is proposed to reasonably estimate a representative annual input load of antibiotics and other micropollutants.

The adaptation of nitrifying microorganisms to inhibiting substances at meso- and psychrophilic temperature conditions.

This paper deals with adaption capacity of nitrifiers to allylthiourea (ATU) as a model inhibitor at two temperature levels. Nitrifying communities were developed at 15 (BM15) and 30 °C (BM30). The activity of the nitrifiers was determined by using short-time respiration (STR) tests, oxygen monitoring and in-situ measurements. The oxygen monitoring provided information about the temperature-dependent time delay between the dosage of NH4(+)-N or ATU and reaching its characteristic level of effect. The greatly scattered results from the STR tests for BM15 were thus explained by the time delay, which was two to three times higher than for BM30. Furthermore, combining the results of oxygen-monitoring and in-situ measurements it can be stated that an adaption to ATU at psychrophilic temperature conditions was not achieved, whereby up to 40% of nitrification was sustained for BM30 at an ATU-concentration over 7 mg/l. The nitrification by BM15 did not start until ATU was degraded to 1-2 mg/l, the typical inhibition concentration for ATU. Hence, the results indicate a population drift to adapted nitrifiers at mesophilic conditions and ATU-degrading microorganisms at psychrophilic temperature conditions, which can have a considerable influence on domestic wastewater treatment in cold climates receiving industrial effluents.

Temperature as an alternative tracer for the determination of the mixing characteristics in wastewater treatment plants.

The hydraulic characteristics, i.e. the residence time distributions, of wastewater treatment plant reactors are usually determined using conventional tracers. This paper aims to present an alternative approach based on wastewater temperature. The step in temperature change, e.g. from stormwater events with cold rainwater, is used as a tracer signal. The method was verified using lab- and pilot-scale tests that showed very good agreement of the time series estimated both with conventional and temperature tracer methods. Results from lab-scale tests exhibit a zone with a minor water exchange of about 10% of the volume of all reactors, while the respective zone in the pilot-scale tests was estimated at about 30% of the total volume. The short-circuit flow was more than 50% of the inflow resulting from gaps between the walls inside the reactor cascade. An application example shows the importance of reliable residence time distribution underlying activated sludge modelling and the uncertainty associated with neglecting the determination of appropriate flow-through characteristics.