Salar Haghighatafshar

Potential for nutrient recovery and biogas production from blackwater, food waste and greywater in urban source control systems.

In the last decades, the focus on waste and wastewater treatment systems has shifted towards increased recovery of energy and nutrients. Separation of urban food waste (FW) and domestic wastewaters using source control systems could aid this increase; however, their effect on overall sustainability is unknown. To obtain indicators for sustainability assessments, five urban systems for collection, transport, treatment and nutrient recovery from blackwater, greywater and FW were investigated using data from implementations in Sweden or northern Europe. The systems were evaluated against their potential for biogas production and nutrient recovery by the use of mass balances for organic material, nutrients and metals over the system components. The resulting indicators are presented in units suitable for use in future sustainability studies or life-cycle assessment of urban waste and wastewater systems. The indicators show that source control systems have the potential to increase biogas production by more than 70% compared with a conventional system and give a high recovery of phosphorus and nitrogen as biofertilizer. The total potential increase in gross energy equivalence for source control systems was 20–100%; the greatest increase shown is for vacuum-based systems.

Hygienization of sludge through anaerobic digestion at 35, 55 and 60 °C

Legislation in Sweden and the European Union concerning the use of sewage sludge in agriculture is under revision and future concentration limits for pathogens in treated sludge are likely to be expected. The aim of this study was to evaluate the hygienization of Salmonella, Escherichia coli, Enterococcus and Clostridium perfringens through continuous anaerobic digestion at 35, 55 or 60 °C, as well as to investigate process stability and methane production at 60 °C. The results indicated that digestion at 55 or 60 °C with a minimum exposure time of 2 h resulted in good reduction of Salmonella, E. coli and Enterococcus and that anaerobic digestion could thus be used to reach the concentration limits suggested for the EU, as well as Sweden. Furthermore, stable continuous anaerobic digestion of sludge was achieved at 60 °C, albeit with 10% less methane production compared to digestion at 35 and 55 °C.

Efficiency of blue-green stormwater retrofits for flood mitigation – Conclusions drawn from a case study in Malmö, Sweden

Coupled one-dimensional (1D) sewer and two-dimensional (2D) overland flow hydrodynamic models were constructed to evaluate the flood mitigation efficiency of a renowned blue-green stormwater retrofit, i.e. Augustenborg, in Malmö, Sweden. Simulation results showed that the blue-green stormwater systems were effective in controlling local surface flooding in inner-city catchments, having reduced the total flooded surfaces by about 70%. However, basement flooding could still be a potential problem depending on the magnitude of the inflows through combined sewer from upstream areas. Moreover, interactions between blue-green retrofits and the surrounding pipe-system were studied. It was observed that the blue-green retrofits reduced the peak flows by approximately 80% and levelled out the runoff. This is a substantial advantage for downstream pipe-bound catchments, as they do not receive a cloudburst-equivalent runoff from the retrofitted catchment, but a reduced flow corresponding to a much milder rainfall. Blue-green retrofits are more effective if primarily implemented in the upstream areas of a pipe-bound catchment since the resulting reduced runoff and levelled out discharge would benefit the entire network lying downstream. Implementing blue-green retrofits from upstream towards downstream can be considered as a sustainable approach.

Effect of anaerobic digestion at 35, 55 and 60 °C on pharmaceuticals and organic contaminants

The application of treated sewage sludge on farmland is a suggested method for recycling nutrients and reducing demand for commercial fertilizer. However, sludge needs to be safe from possible contaminants which can cause acute and long-term health and environmental problems. Residual pharmaceuticals and organic contaminants are mentioned as emerging threats since wastewater treatment plants are not designed to degrade these substances. The aim of this study was to screen and evaluate the presence, and reduction, of pharmaceuticals and polycyclic aromatic hydrocarbons (PAHs) during anaerobic digestion of mixed primary and waste-activated sludge at 35, 55 and 60 °C and during pasteurization at 70 °C. The study showed the difficulty of analysing pharmaceutical compounds in low concentrations in the sludge matrix. No general reduction of these compounds was seen during treatment, but for individual substances some reduction occurred. The PAHs were generally not reduced during digestion or pasteurization, but for three substances (indeno[1,2,3-cd]pyrene and dibenzo[a,h]anthracene (analysed together) and benzo[g,h,i]perylene) reduction (up to 60%) during digestion was seen. Digestion at 35 and 55 °C resulted in about the same order of reduction of the three individual PAHs, which was higher than for digestion at 60 °C.

Laboratory-scale assessment of vacuum-degassed activated sludge for improved settling properties

ABSTRACT Vacuum degassing of activated sludge was tested at eight different Swedish wastewater treatment plants with laboratory-scale equipment in batch mode in order to evaluate its efficiency on improvement of sludge compaction and settling properties. The results show that the efficiency of the degassing technique is mainly dependent on the initial sludge volume index (SVI) of the target sludge which was found to be related to its process configuration. Facilities with full activated sludge-based nitrogen removal processes, including both nitrification and denitrification, had high SVIs (>300 mL g−1) and were strongly affected by vacuum degassing with reduction of SVI up to 30%. Nitrogen removal facilities also including biological phosphorus removal showed better compaction and settling properties with relatively lower SVIs and were affected to a lesser extent by degassing with SVI reduction of 10–20%. Wastewater treatment plants without full biological nitrogen removal, lacking either nitrification or denitrification (or both) processes in the activated sludge had the lowest SVIs observed with almost no effect of vacuum degassing.

Modeling of anaerobic digestion with a focus on estimation of hydrolysis constants at 35, 55, and 60°C

Hydrolysis constants of mixed sludge at 35, 55, and 60 °C were found to be 0.32, 0.44, and 0.50 1/d, respectively, in pilot-scale, semicontinuously operated anaerobic digesters. The hydrolysis constants and estimated chemical oxygen demand fractions in the feed were introduced to a mathematical model for anaerobic digestion published by Siegrist et al. (2002), which is similar to Anaerobic Digestion Model No. 1. First-order and Monod-type kinetics were tested for estimation of hydrolysis constants. The applied kinetics were found to affect the outcome of the regression study. Moreover, the free ammonia inhibition model was excluded for both propionate oxidation and acetate conversion, thanks to the apparent acclimatized biomass. No substantial accumulation of volatile fatty acids was observed in the reactors at 35, 55, and 60 °C, corresponding to free ammonia nitrogen concentrations of about 20, 110, and 130 g N/m³, respectively.