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.

For successfully operating a vertical flow constructed wetland, the uniform distribution of wastewater on the surface of the soil filter is essential. In research however, this aspect is often overlooked. This study presents a methodology for assessing discharge uniformity from perforated pipe systems via hydraulic modeling. First, the requirements and conditions for the simulation of perforated pipe systems are investigated and the model basics are explained. Then the whole process of model built-up, calibration, application and analysis is presented and discussed. The modeling is done by the software EPANET and supported by pressure measurements in the pipe system of a small wetland treating domestic sewage. A crucial factor in the modeling process is the choice of loss coefficients in dividing junctions. Different approaches for calculating such coefficients are compared. Model calibration is undertaken via the multicriterion optimization algorithm NSGA-II. By calibrating two parameters, a reasonable goodness of fit with the measured pressure values was achieved. Model results show that distribution uniformity of the pipe system in question is poor. An outlook on potential applications of hydraulic modeling of perforated pipe systems in vertical flow constructed wetlands is given.

Wastewater from factories producing polysulfone-based membranes mainly contains the used organic solvent, i.e., dimethylacetamide (DMAc). Due to the environmental impact of DMAc, wastewater treatment is mandatory. Several biological treatment options based on the activated sludge process are described in the literature. Due to artificial aeration, these techniques have high energy requirements. Near-nature processes such as vertical flow constructed wetlands (VF wetlands) have a low energy demand, high tolerance to load fluctuations, and low maintenance requirements. Therefore, high-loaded, two-stage VF wetlands are an efficient option for treating wastewater. However, constructed wetlands have so far only been used to a limited extent for the treatment of industrial wastewater. In the present study, the ability of laboratory-scale, high-load, two-stage VF wetlands to treat DMAc was investigated. This included their DMAc degradation efficiency and corresponding pathways, removal of the total organic carbon (TOC), nitrification and denitrification of the nitrogen, as well as the ecotoxicological effects (mutagenicity, genotoxicity, reactive oxygen species) of untreated and treated wastewater. The focus was to determine the effect of different grain size distributions on removal rates, the maximum inflow loading, and the effect of high inflow concentrations on effluent concentrations. In general, DMAc was completely degraded using VF wetlands, with dimethylamine (DMA) identified as the main intermediate. TOC removal rates reached more than 99%. The nitrogen bound to DMAc was completely nitrified. However, the start-up of the VF wetlands without seeded filter material temporarily leads to high nitrite accumulation. This may affect the mutagenicity of the treated wastewater. The results show that high-loaded, two-stage VF wetlands are an effective option for treating wastewater containing DMAc with higher efficiency than comparable biological processes.