Small-scale electrical power generation (<100 kW) from biogas plants to provide off-grid electricity is of growing interest. Currently, gas engines are used to meet this demand. Alternatively, more efficient small-scale solid oxide fuel cells (SOFCs) can be used to enhance electricity generation from small-scale biogas plants. Most electricity generators require a constant gas supply and high gas quality in terms of absence of impurities like H 2S. Therefore, to efficiently use the biogas from existing decentralized anaerobic digesters for electricity production, higher quality and stable biogas flow must be guaranteed. The installation of a biogas upgrading and buffer system could be considered; however, the cost implication could be high at a small scale as compared to locally available alterna-tives such as co-digestion and improved digester operation. Therefore, this study initially describes relevant literature related to feedstock pre-treatment, co-digestion and user operational practices of small-scale digesters, which theoretically could lead to major improvements of anaerobic digestion process efficiency. The theoretical preamble is then coupled to the results of a field study, which demonstrated that many locally available resources and user practices constitute frugal innovations with potential to improve biogas quality and digester performance in off-grid settings. @en

Particle-bubble collisions in dissolved air flotation (DAF) systems play a crucial role in the removal of total suspended solids (TSS). DAF particle-bubble collision models incorporate factors such as particle diameters, charge and density, bubble diameters, and collision factors. The challenge lies in accounting for the wide range of particle and bubble sizes and obtaining complex model inputs. To address this, a simplified model for TSS removal in DAF units was established using low-cost laboratory measurements, including particle size distribution and density. Additionally, microbubble diameter profiles were derived from bubble velocities using particle image velocimetry software (PIV). Six independent variables, encompassing influent particle characteristics (such as particle size distribution and density) and DAF running characteristics (temperature, contact zone detention time, inflow and recycle flows), were employed in the simplified model. The model's accuracy was evaluated using a laboratory-scale DAF system with two different influents: Delft canal water and anaerobic sludge. The predicted TSS removal from the simplified model aligned well with the laboratory-scale DAF results, yielding removal efficiencies of 68 ± 1 % and 77 ± 3 % for Delft canal water and anaerobic sludge, respectively. Furthermore, when the simplified model was applied to two full-scale DAF systems, it successfully identified an underperforming system (DAF2) with a TSS removal efficiency of 91 %, contrasting with the theoretical removal model-predicted efficiency of 98 %. This study highlights the utility of combining bubble size distribution measured by PIVlab and particle size distribution obtained using FIJI-ImageJ as an economical and efficient approach to acquiring the necessary inputs for predicting TSS removal in DAF systems.@en

This study investigates the effects, conversions, and resistance induction, following the addition of 150 μg·L−1 of two antibiotics, sulfamethoxazole (SMX) and trimethoprim (TMP), in a laboratory-scale micro-aerated anaerobic membrane bioreactor (MA-AnMBR). TMP and SMX were removed at 97 and 86%, indicating that micro-aeration did not hamper their removal. These antibiotics only affected the pH and biogas composition of the process, with a significant change in pH from 7.8 to 7.5, and a decrease in biogas methane content from 84 to 78%. TMP was rapidly adsorbed onto the sludge and subsequently degraded during the long solids retention time of 27 days. SMX adsorption was minimal, but the applied hydraulic retention time of 2.6 days was sufficiently long to biodegrade SMX. The levels of three antibiotic-resistant genes (ARGs) (sul1, sul2, and dfrA1) and one mobile genetic element biomarker (intI1) were analyzed by qPCR. Additions of the antibiotics increased the relative abundances of all ARGs and intI1 in the MA-AnMBR sludge, with the sul2 gene folding 15 times after 310 days of operation. The MA-AnMBR was able to reduce the concentration of antibiotic-resistant bacteria (ARB) in the permeate by 3 log.@en

This study reports the effects of microaeration on a laboratory-scale AnMBR (MA-AnMBR) fed with synthetic concentrated domestic sewage. The imposed oxygen load mimics the oxygen load coming from a dissolved air flotation (DAF) unit, establishing an anaerobic digester-DAF (AD-DAF) combination with sludge recycling. Results showed a reduced COD concentration in the MA-AnMBR permeate compared with the AnMBR permeate, from 90 to 74 mgCOD L–1, and a concomitant 27% decrease in biogas production. The MA-AnMBR permeate ammonium (NH4+) concentration increased by 35%, to 740 mgNH4+-N L–1, indicating a rise in the hydrolytic capacity. Furthermore, the MA-AnMBR biomass seemingly adapted to an increased oxygen load, which corresponded to 1% of the influent COD load (approximately 55 mLO2 d–1). Concomitantly, an increase in the superoxide dismutase activity (SOD) of biomass was detected. Meanwhile, negligible changes were observed in the specific methanogenic activity (SMA) of the microaerated biomass that was subjected to an oxygen load equivalent to 3% of the influent COD load in batch tests. The obtained results showed that an AD-DAF system could be a promising technology for treating concentrated domestic wastewater, improving sewage sludge hydrolysis, and overall organic matter removal when compared to an AnMBR.@en

The Barapullah drain crosses through New Delhi, India, and transports millions of cubic meters of stormwater, municipal sewage and industrial sewage to the Yamuna River. Seasonal variations and ambiguous annual discharges cause 20-fold fluctuations in hydraulic flows, pollutants type and concentration. Furthermore, New Delhi is among the most densely populated areas on the planet, with limited surface area and high water stress. Dissolved Air Flotation (DAF) units are known to be highly compact, robust, and an efficient suspended solids separation technology that enables further water recovery in a treatment train. Thus, a down-scaled column DAF was designed and used to determine the total suspended solids removal efficiencies, under different influent conditions. Three influents that resemble the Barapullah drain seasonal variations in composition, and a fourth that imitates the feed of DAF when located after an anaerobic bioreactor were tested. A total of 60 batch DAF experiments were completed and used to assess seven independent control variables for DAF operation, which are influent Total Suspended Solids (TSS), pH, temperature, DAF particles residence time, white water pressure, coagulants and flocculants concentration, and coagulation and flocculation time. Results showed that the down-scaled DAF could be steered from low to high removal efficiencies, comparable to full-scale systems. Maximum TSS removal varied between 92 and 96%. The effect and statistical relevance of the different performance variables on the measured separation efficiencies depended on the influent type. All variables, except temperature and pH, had a significant performance effect with a p-value below 0.1, for at least one influent. Pressure had a positive effect on separation efficiency, due to its importance in bubble formation. Moreover, the down-scaled DAF system had low removal efficiency for particles with spherical shapes, and diameters below 10 µm. Based on the high TSS removal for all tested influents, and the effect of the studied control variables, a full-scale DAF could efficiently remove the suspended solids of the Barapullah drain. The unit robustness for different flows and pollutant concentrations, and small footprint, show DAF suitability as part of a treatment train for water recovery, in densely populated areas.@en

In the context of a worldwide scenario characterized by a progressively expanding human population, the combining effects of climate change, escalating water stress, and the degradation of freshwater resources, water reclamation has emerged as a viable solution to alleviate the critical issue of water scarcity. Several streams around the world are subjected to a wide range of pollutants concentration and water-born pathogens, like antibiotic-resistant bacteria (ARB), due to human activity. The latter can be considered as a global emerging threat, due to its potential to deteriorate the human health system. Thus, adequate treatment of these polluted streams is needed to overcome water scarcity. While anaerobic membrane bioreactors (AnMBR) systems are a promising anaerobic digestion (AD) technology to treat municipal and concentrated wastewater, the application of membranes to separate solids from the bioreactor broth also has considerable constraints. An alternative physical separation method could be used to overcome the AnMBR limitations. Replacing the membrane unit of an AnMBR with a dissolved air flotation (DAF) system, and returning the flotation layer to the anaerobic reactor, may ensure high total suspended solids (TSS) retention while overcoming the membrane limitations. However, the oxygen-saturated flotation layer and the overall introduction of oxygen into the reactor through the DAF may negatively impact the anaerobic conversion process. This dissertation investigates the potential to use an AD coupled with a DAF system (AD-DAF) as a pre-treatment technology, specifically for the treatment of drain- and wastewater that mimics the ever-changing conditions of the Barapullah drain in New Delhi. Since testing an AD-DAF system on a laboratory-scale is not practically feasible, due to the constraints in downscaling a DAF unit, the implications of coupling these two technologies were assessed in two different systems: a column bench-scale DAF unit, and a lab-scale micro-aerated anaerobic membrane bioreactor (MA-AnMBR). To begin with, a data-driven experimental DAF model was developed to predict TSS removal. Input values for the experimental model were particle and bubble characteristics. The experimental model outcomes were verified in a bench-scale column DAF and two full-scale DAF systems. Results showed a predicted TSS removal aligned with the measured one of Delft canal water, anaerobic sludge, and DAF2 influents, 68 ± 1% vs. 66-96%, 77 ± 3% vs. 68-92%, and 98 ± 1% vs. 96± 1%, respectively.Afterwards, the bench-scale DAF was used to investigate the removal of suspended solids under four different influent conditions and seven DAF independent control variables (influent TSS, pH, temperature, DAF particles residence time, white water pressure, coagulants and flocculants concentration and mixing time). The influents simulated the Barapullah drain conditions under 1) dry and 2) monsoon times, and 3) close or 4) far from the pollution source. The results obtained indicated that TSS removal efficiency on the bench-scale DAF unit could mimic a full-scale system and that a DAF can remove over 90% of TSS for the four different tested influents. On the other hand, the effect of the performance variables altered depending on the influent type, with pressure showing a positive influence on the separation efficiency.Secondly, to assess the effect of coupling the DAF system with AD, a lab-scale AnMBR system was subjected to an oxygen load similar to the one used on a DAF unit. The effects of the oxygen load were compared to a fully anaerobic system, and the MA-AnMBR performance was assessed, for removal of organic matter, biogas production, nutrient concentration, operation and maintenance, and removal of two antibiotics sulfamethoxazole, SMX, and trimethoprim, TMP). Results showed a slight significant increase in COD removal, from 98.2 to 98.5%, and an increase of 35% in the ammonium concentration in the MA-AnMBR permeate, which indicated improved hydrolysis. Furthermore, biogas production decreased by 27%, but methane concentration on both MA-AnMBR and AnMBR was high (85%). Micro-aeration of the AnMBR had no negative effect in the removal of the tested antibiotics, which have a preferred anaerobic degradation pathway. TMP was rapidly adsorbed onto the sludge biomass and then degraded due to the long solids’ retention time (27 days). SMX adsorption was minimal, but the system hydraulic retention time of 2.6 days allowed its biodegradation. The addition of SMX and TMP led to an increase in the relative abundance of all studied anti-microbial resistant genes (ARGs) ( sul1, sul2, and dfrA1) and one mobile genetic element (intI1) in the MA-AnMBR sludge. Furthermore, the presence of antibiotic-resistant bacteria and antibiotic-resistance genes in the reactor permeate indicated that further treatment was needed. The outcomes obtained in this dissertation showed that an AD-DAF system has the potential to effectively remove total suspended solids under different influent conditions, and that the added oxygen load could improve hydrolysis with minimal impacts on the anaerobic conversion processes.@en