Floating immobilized TiO2 catalyst for the solar photocatalytic treatment of micro-pollutants within the secondary effluent of wastewater treatment plants.

Floating immobilized spherical titanium dioxide catalysts were used to degrade micro-pollutants by solar photocatalysis. The degradation of the micro-pollutants was performed in the secondary effluent of a wastewater treatment plant. During the experimental period, the continuous measurement of the solar ultraviolet (UV) radiation intensity was performed. The micro-pollutants were degraded to an average of 55% after 9 h of irradiation. A substance-specific degradation affinity was found, whereby degradation rates varied by a factor of up to 3.5. The substance-specific adsorption behavior was identified as a major limitation of the reaction performance. With an increasing influence of adsorption limitation, the degradation kinetics changed from the pseudo-first order to pseudo-zero order. A correlation between degradation rate and solar irradiance could only be found for substances with high degradation/adsorption affinity. For diclofenac, a 95% degradation rate could be achieved at a radiation dose of approximately 190 mWh/m². The investigated technology represents a promising possibility for a minimally invasive extension of wastewater treatment plants. Possibilities of implication were estimated and discussed within this work, whereby possibilities arise for large-scale as well as decentral treatment plants.

Photocatalytic ozonation in an immersion rotary body reactor for the removal of micro-pollutants from the effluent of wastewater treatment plants.

Carrier-bound titanium dioxide catalysts were used in a photocatalytic ozonation reactor for the degradation of micro-pollutants in real wastewater. A photocatalytic immersion rotary body reactor with a 36-cm disk diameter was used, and was irradiated using UV-A light-emitting diodes. The rotating disks were covered with catalysts based on stainless steel grids coated with titanium dioxide. The dosing of ozone was carried out through the liquid phase via an external enrichment and a supply system transverse to the flow direction. The influence of irradiation power and ozone dose on the degradation rate for photocatalytic ozonation was investigated. In addition, the performance of the individual processes photocatalysis and ozonation were studied. The degradation kinetics of the parent compounds were determined using liquid chromatography tandem mass spectrometry. First-order kinetics were determined for photocatalysis and photocatalytic ozonation. A maximum reaction rate of the reactor was determined, which could be achieved by both photocatalysis and photocatalytic ozonation. At a dosage of 0.4 mg O3/mg DOC, the maximum reaction rate could be achieved using 75% of the irradiation power used for sole photocatalysis, allowing increases in the energetic efficiency of photocatalytic wastewater treatment processes. The process of photocatalytic ozonation is suitable to remove a wide spectrum of micro-pollutants from wastewater.

Behavior of matrix parameters and their correlation to micro-pollutant degradation during treatment of real wastewater by carrier-bound photocatalytic ozonation.

Immobilized titanium dioxide catalysts were used within a photocatalytic immersion rotary body reactor, which was connected to a substream ozonation unit to remove micro-pollutants from wastewater. Within this work data on the behavior of cumulative parameters during treatment of wastewater by photocatalysis and photocatalytic ozonation are provided. The investigated parameters are spectral absorption coefficient at 254 nm (SAC254), total organic carbon (TOC) and chemical oxygen demand (COD). All experiments were carried out using secondary effluent from the same wastewater treatment plant. For the parameter SAC254, consistent concentration curves and dependencies to operational parameters of the experimental system could be measured. The measurements of the parameters TOC and COD showed greater uncertainties, although basic trends could nonetheless be observed. A good linear correlation (R2 < 0.85) between the reduction of SAC254 and 8 micro-pollutants for photocatalysis and photocatalytic ozonation was found. This confirms the suitability of the SAC254 as a control parameter for a large-scale application of a photocatalytic 4th treatment stage. A linear correlation between measured TOC and COD degradation rates was possible with a coefficient of determination of 0.58-0.86. The simultaneous decrease of TOC and COD is an indicator for a mineralization of the treated wastewater matrix.

A Research Agenda for the Future of Urban Water Management: Exploring the Potential of Nongrid, Small-Grid, and Hybrid Solutions.

Recent developments in high- and middle-income countries have exhibited a shift from conventional urban water systems to alternative solutions that are more diverse in source separation, decentralization, and modularization. These solutions include nongrid, small-grid, and hybrid systems to address such pressing global challenges as climate change, eutrophication, and rapid urbanization. They close loops, recover valuable resources, and adapt quickly to changing boundary conditions such as population size. Moving to such alternative solutions requires both technical and social innovations to coevolve over time into integrated socio-technical urban water systems. Current implementations of alternative systems in high- and middle-income countries are promising, but they also underline the need for research questions to be addressed from technical, social, and transformative perspectives. Future research should pursue a transdisciplinary research approach to generating evidence through socio-technical "lighthouse" projects that apply alternative urban water systems at scale. Such research should leverage experiences from these projects in diverse socio-economic contexts, identify their potentials and limitations from an integrated perspective, and share their successes and failures across the urban water sector.

Hydrogen peroxide-assisted photocatalytic water treatment for the removal of anthropogenic trace substances from the effluent of wastewater treatment plants.

Supported titanium dioxide catalysts were used in a photocatalytic flat cell reactor to remove organic micropollutants from real wastewater. Catalysts based on stainless steel mesh with a porous coating made of titanium dioxide nanoparticles with predominantly anatase modification were used. The influence of the retention time, and light output, and the effect of hydrogen peroxide on the degradation were examined. The kinetics of the degradation of the parent substances was determined by liquid chromatography-tandem mass spectrometry. As a result, first-order degradation kinetics could be confirmed for all substances. The irradiance had no linear influence on the degradation of the compounds. Hydrogen peroxides were added to the wastewater to be treated, as electron acceptors and boosters, and alone had no great oxidative effect on the parent substances. The combination of photocatalysis with the addition of hydrogen peroxide as an electron acceptor had great synergetic effects which can reduce the required energy of the process through a short retention time. The process is suitable for the removal of micropollutants from wastewater.

Characterization of domestic graywater and graywater solids.

The knowledge of loads and concentrations is fundamental for the design of graywater treatment units, but the data on the characteristics of graywater and in particular graywater solids are weak. As general design values regarding graywater treatment facilities are not available for Germany, the objective of this article is to elaborate the characteristics of graywater and graywater solids. This paper describes the results of six sampling campaigns carried out on graywater systems in the German cities Berlin, Lübeck and Kiel. All graywater samples were collected proportional to the flow and the graywater solids were gathered separately. The collected data include graywater volumes and characteristics regarding the organic pollution (chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD5)) and nutrients (total nitrogen (TN), total phosphorus (TP)). The graywater volume fluctuated depending on the location. The specific average flow was 68 litre per inhabitant per day (L/inh.d). Inhabitant-specific loads of 49.3 gCODt/inh·d, 28 gBOD5/inh.d, 1 gTNt/inh.d and 0.38 gTPt/inh.d (subscript 't' = total) were found. Information about the composition of graywater solids in terms of quantity and quality is seriously lacking. Therefore, graywater solids were examined with respect to organic matter (COD) and nutrients (TN, TP). The contribution of graywater solids with particle sizes over 200 microns in relation to the total inhabitant-specific load was approximately 3-8% depending on the parameter. The qualitative and quantitative characteristics of the investigated graywater fractions may serve as a base for the estimation of design values.

On the design and operation of primary settling tanks in state of the art wastewater treatment and water resources recovery.

In state of the art wastewater treatment, primary settling tanks (PSTs) are considered as an integral part of the biological wastewater and sludge treatment process, as well as of the biogas and electric energy production. Consequently they strongly influence the efficiency of the entire wastewater treatment plant. However, in the last decades the inner physical processes of PSTs, largely determining their efficiency, have been poorly addressed. In common practice PSTs are still solely designed and operated based on the surface overflow rate and the hydraulic retention time (HRT) as a black box. The paper shows the results of a comprehensive investigation programme, including 16 PSTs. Their removal efficiency and inner physical processes (like the settling process of primary sludge), internal flow structures within PSTs and their impact on performance were investigated. The results show that: (1) the removal rates of PSTs are generally often underestimated in current design guidelines, (2) the removal rate of different PSTs shows a strongly fluctuating pattern even in the same range of the HRT, and (3) inlet design of PSTs becomes highly relevant in the removal efficiency at rather high surface overflow rates, above 5 m/h, which is the upper design limit of PSTs for dry weather load.

Phosphorous recovery from a novel recirculating aquaculture system followed by its sustainable reuse as a fertilizer.

Phosphorus (P) is an essential element for life that is introduced through feed in modern aquaculture-the fastest growing food production sector. P can also be a source of environmental contamination and eutrophication if mistreated. Fish assimilate only 20-40% of the applied P; the rest is released into the water. The goals of this research were to study the fate of P in a novel intensive near-zero discharge (<1%) recirculating aquaculture system (RAS). We also tested means to recover and reuse the removed P. Water, sludge and the microbial communities in the different treatment units of the system were analyzed. The treated sludge was tested as a potential substitute for P fertilization in a planter experiment. Of the applied P, 29.5% was recovered by fish, 69.8% was found in the fish sludge and 3.8% was released into the water as soluble reactive P. The P concentration in the fish tank remained stable, likely due to its uptake by denitrifying polyphosphate-accumulating organisms and its precipitation in the RAS's anaerobic reactor. Thus, only 1.5% of the applied P was discharged as effluent, and 69% recovered. The dominant minerals were from the apatite group, followed by the struvite family. Differences in mineral abundance between thermodynamic prediction and actual findings were most probably due to biomineralization by bacteria. Similar plant biomass was recorded for the commercial and digested-sludge fertilization treatments. Biological P removal and recovery from RAS was successfully studied and demonstrated.