Seeking to enhance the bioenergy of municipal sludge: Effect of alkali pre-treatment and soluble organic matter supplementation

The aim of this research is to enhance the mesophilic anaerobic digestion of municipal sludge from Cadiz-San Fernando (Spain) wastewater treatment plant at 20 days hydraulic retention time (HRT). Two different strategies were tested to improve the process: co-digestion with the addition of soluble organic matter (1% v/v); and alkali sludge pre-treatment (NaOH) prior to co-digestion with glycerine (1% v/v). Methane production (MP) was substantially enhanced (from 0.36 ± 0.09 L CH4 l/d to 0.85 ± 0.16 L CH4 l/d), as was specific methane production (SMP) (from 0.20 ± 0.05 L CH4/g VS to 0.49 ± 0.09 L CH4/g VS) when glycerine was added. The addition of glycerine does not seem to affect sludge stability, the quality of the effluent in terms of pH and organic matter content, i.e. volatile fatty acids (VFA), soluble organic matter and total volatile solid, or process stability (VFA/Alkalinity ratio < 0.4). Alkali pre-treatment prior to co-digestion resulted in a high increase in soluble organic loading rates (more than 20%) and acidification yield (more than 50%). At 20 days HRT, however, it led to overload of the system and total destabilization of the mesophilic anaerobic co-digestion of sewage sludge and glycerine

Effects of several inocula on the biochemical hydrogen potential of sludge-vinasse co-digestion

The influence of the inoculum on the Biochemical Hydrogen Potential test (BHP) was investigated. Thermophilic BHP from sludge-vinasses co-digestion (50:50) was studied employing three types of inocula: Acidogenic Inoculum, Sludge Inoculum and Thermal Sludge Inoculum. The maximum hydrogen yield was obtained with a sludge inoculum (177 mL H2/g VSadded). This yield was 21 and 36% higher than for acidogenic inoculum and thermal sludge inoculum, respectively. The results revealed that the choice of inoculum had significant impact on the hydrogen yield and the sludge inoculum is the most beneficial for BHP tests. The percentages between Eubacteria:Archaea increased from 59.2:40.8 to 92.0:9.0 during BHP tests using the sludge inoculum while it remained stablish in the others cases around 50:50. Furthermore, hydrogen production was accompanied by the generation of volatile fatty acids, mainly acetic, butyric and propionic acids. There were no differences in the rate of hydrogen production in any of the BHP

Producció d’àcids grassos volàtils mitjançant residus de fangs actius i de menjar per a produir bioplàstics

Treballs Finals de Màster d'Enginyeria Química, Facultat de Química, Universitat de Barcelona. Curs: 2021-2022. Tutors: Joan Dosta Parras, Sergi Astals GarciaFossil fuel exhaustion, increasing greenhouse gases emissions and population growth, among many other issues, are leading to many environmental problems which require a transformation of the production system and waste management including wastewater treatment plants (WWTPs). Hence, the end-of-pipe processes for organic wastes treatment are being converted into resource recovery facilities that produce value-added products. Anaerobic biological processes using mixed cultures can handle the variability of organic wastes: for example, these wastes could be initially converted to volatile fatty acids (VFAs) through acidogenic fermentation and the remaining part (non-VFA organic matter) could be directed to anaerobic digestion to produce biogas. VFAs have multiple applications and one of them is its use as carbon source for polyhydroxyalkanoates (PHA) production. PHA are value-added products mainly composed by polyhydroxybutyrate (PHB) and/or polyhydroxyvalerate (PHV), that can be obtained using mixed microbial cultures in 4 phases: acidogenic fermentation, selection of PHA-storing microorganisms, accumulation of PHA using selected biomass and PHA extraction. In this Master thesis, the first 3 stages of the PHA production process using organic wastes (namely, the acidogenic fermentation, the selection of PHA-storing microorganisms and the PHA accumulation) are studied. The effect of pH on food waste (FW) and wasted activated sludge (WAS) co-fermentation was studied using batch tests and semi-continuous experiments at mesophilic conditions (35 ºC). The pH control in semi-continuous fermenters was difficulted by continuous foaming events. Moreover, PHA production using VFA-rich wastewater (simulating the effluent resulting from an acidogenic fermentation of the organic fraction of municipal solid wastes (OFMSW)) and different selection strategies (one using aerobic feast-famine with nitrogen depletion during feast and the other applying only aerobic feast-famine regime). Furthermore, the VFA profile obtained along the suitable operation of co-fermenters is compared with the synthetic stream used to assess PHA production. The acidogenic fermentation unit was monitored with VFA profile and distribution, pH, chemical oxygen demand and soluble chemical oxygen demand (COD and sCOD), total ammonium nitrogen (TAN) concentration, total and volatile solids (TS and VS) and alkalinity. Batch tests were performed in glass-bottles filled with 150 mL of fixed proportions of WAS and FW (75:25 on VS basis) and using a lab-scale semi-continuous fermenter’s effluent to test the influence of pH in substrates and an operating fermenter, respectively. Furthermore, 2 semi-continuous fermenters with 1.75 L of working volume were operated for 46 days using fixed proportions of WAS and FW (65:35 on VS basis), organic loading rate (OLR) (11 g VS kg-1 d-1), hydraulic retention time (HRT) (3 d) and mixing at 80 rpm. Main VFAs resulted from batch tests and fermenters were acetic acid (30%), butyric acid (30%) and propionic acid (20%). Higher pH showed an increased VFA yield as the solubilisation of organic matter (hydrolysis) was enhanced. Acetic acid consumption in fermenters was experimented and reduced by changing operational parameters (reduction in FW and HRT). Due to foam formation, pH control in semi-continuous operation could not been studied although different strategies were tested to minimise foam (better homogenisation, discharging foams using effluent tubes and lowering HRT and FW proportion). Regarding to lab-scale PHA production, the monitoring of cycles was performed by recording dissolved oxygen (DO) profile, TAN and VFA concentrations, total and volatile suspended solids (TSS and VSS) and pH. VFA-rich synthetic influent with a concentration of 3.5 g COD L-1 for both selection and accumulation phases was used. Biomass selection was performed with a selection sequential batch reactor (sSBR) at 35 ºC and 80 rpm agitation with aerobic conditions using diffusors connected to air pumps and net-air. Furthermore, for accumulation tests a 1 L capacity glass reactor at 35 ºC, agitation at 80 rpm and air supply system were used. Experimental results showed that if double selection strategy (aerobic feast-famine plus nitrogen decoupling in feast) higher PHA content in purge was obtained (30% on suspended solid (SS) basis) along with higher contents of PHA during accumulation (50% on SS basis) compared to a single selection strategy (only aerobic feast-famine regime) with PHA contents of 11% and 38% (SS basis), respectively. Similar PHA compositions were obtained through selection and accumulation phases with the 90% in PHB and 10% in PHV. To sum up, raising pH increases VFA yields in acidogenic fermentation as consequence of hydrolysis and organic matter solubilisation enhancement. Moreover, increasing pH earlier in fermentation batch tests derives in higher VFA production. Due to PHA production, although both strategies selected the biomass successfully, double selection results in higher PHA accumulation potential. It is expected a suitable PHA production if fermenter’s effluents are used (removing previously the nitrogen content) because of the higher ratios CODVFA sCOD-1 and the similar composition of VFAs

A critical review of resource recovery from municipal wastewater treatment plants : market supply potentials, technologies and bottlenecks

In recent decades, academia has elaborated a wide range of technological solutions to recover water, energy, fertiliser and other products from municipal wastewater treatment plants. Drivers for this work range from low resource recovery potential and cost effectiveness, to the high energy demands and large environmental footprints of current treatment-plant designs. However, only a few technologies have been implemented and a shift from wastewater treatment plants towards water resource facilities still seems far away. This critical review aims to inform decision-makers in water management utilities about the vast technical possibilities and market supply potentials, as well as the bottlenecks, related to the design or redesign of a municipal wastewater treatment process from a resource recovery perspective. Information and data have been extracted from literature to provide a holistic overview of this growing research field. First, reviewed data is used to calculate the potential of 11 resources recoverable from municipal wastewater treatment plants to supply national resource consumption. Depending on the resource, the supply potential may vary greatly. Second, resource recovery technologies investigated in academia are reviewed comprehensively and critically. The third section of the review identifies nine non-technical bottlenecks mentioned in literature that have to be overcome to successfully implement these technologies into wastewater treatment process designs. The bottlenecks are related to economics and value chain development, environment and health, and society and policy issues. Considering market potentials, technological innovations, and addressing potential bottlenecks early in the planning and process design phase, may facilitate the design and integration of water resource facilities and contribute to more circular urban water management practices

Potential and limitations of co-fermentation: A review

Màster d'Enginyeria Ambiental, Facultat de Química, Universitat de Barcelona, Curs: 2019-2020, Tutors: Sergi Astals García, Joan Dosta ParrasFermentation is a biotechnological process to generate value from organic waste. During this process, volatile fatty acids (VFA) are obtained as a product, which can be directly used to support other biotechnologies and contribute to the circular economy. However, some substrates present a series of characteristics that are not totally optimal. Co-fermentation is a way to alleviate these drawbacks, which consists on fermenting two or more substrates simultaneously. Co-fermentation is a relatively new approach to the fermentation process as the articles ranging from 2013-2020 account for 77%. A wide range of substrates and combinations have been studied. The more utilised main substrate is waste activated sludge (WAS) followed by primary sludge (PS). Most publications have focused on studying the combination of WAS and food waste (FW) and WAS and agro-industrial (e.g. corn stalk and mushrooms). Most researchers emphasize pH control using chemicals and balancing C/N ratio. Besides, the substrate has been shown to influence the VFA profile as well as the pH. The addition of agro-industrial residue can delay the co-fermentation process due to its high content in lignocellulosic compounds. Overall, other parameters and mixtures should be studied, and more continuous experiments are needed to finish studying co-fermentatio

Review about bioproduction of Volatile Fatty Acids from wastes and wastewaters : Influence of operating conditions and organic composition of the substrate

Acord transformatiu CRUE-CSICVolatile fatty acids (VFAs) are a group of carboxylic acids considered as building block chemicals. Nowadays, commercial production of VFAs is performed using fossil fuel sources. As an alternative, acidogenic fermentation of wastes by mixed microbial cultures (MMC) is starting to be considered as a potential bioproduction process that would replace conventional production processes and contribute to the circular economy. Nevertheless, more research is needed to control the VFA production yields and to precisely drive the fermentation process to the production of a certain VFA or a mixture of VFAs, either by modifying the operational parameters or by appropriately tunning the substrate composition. Following this gap, this review starts screening the metabolic routes that yield VFAs by anaerobic fermentation. Subsequently, the effect of different operational parameters on VFA production yield and VFA composition distribution is extensively discussed depending on the organic composition of the waste in terms of proteins, carbohydrates and lipids. To the best of our knowledge, previous review articles analyzed the impact of these parameters for different types of wastes, but without specifically considering their organic composition in terms of proteins, carbohydrates and lipids. Afterwards, energy-based metabolic models are presented as the one of the best modelling approaches to predict VFA composition. Then, polyhydroxyalkanoates (PHAs) production by MMC is described since it is one of the most promising applications of waste derived VFAs. Finally, we highlight the research gaps that should be further investigated to develop a large scale VFA bioprocess based on MMC platform from waste streams

Utilization of Volatile Fatty Acids from Microalgae for the Production of High Added Value Compounds

Volatile Fatty Acids (VFA) are small organic compounds that have attracted much attention lately, due to their use as a carbon source for microorganisms involved in the production of bioactive compounds, biodegradable materials and energy. Low cost production of VFA from different types of waste streams can occur via dark fermentation, offering a promising approach for the production of biofuels and biochemicals with simultaneous reduction of waste volume. VFA can be subsequently utilized in fermentation processes and efficiently transformed into bioactive compounds that can be used in the food and nutraceutical industry for the development of functional foods with scientifically sustained claims. Microalgae are oleaginous microorganisms that are able to grow in heterotrophic cultures supported by VFA as a carbon source and accumulate high amounts of valuable products, such as omega-3 fatty acids and exopolysaccharides. This article reviews the different types of waste streams in concert with their potential to produce VFA, the possible factors that affect the VFA production process and the utilization of the resulting VFA in microalgae fermentation processes. The biology of VFA utilization, the potential products and the downstream processes are discussed in detail.VOLATILE, a project funded by the European Union’s Horizon 2020 research and innovation program, under the grant agreement no. 720777. The Greek State Scholarships (Postdoc-Research Scholarships IKY). The Hellenic Foundation of Research and Innovation (ELIDEK) financial support (ELIDEK Scholarships for Ph.D. Students)

Enhancing the production of volatile fatty acids by potassium permanganate from wasted sewage sludge: A batch test experiment

Recovering resources from wastewater treatment is vital for the transition from a linear to a circular economy model in the water sector. Volatile Fatty Acids (VFAs) are valuable products among the possible recovered resources. This study investigates the influence of potassium permanganate (KMnO4) addition during acidogenic fermentation of waste activated sludge for enhancing VFAs production. Specifically, different fermentation batch tests with and without KMnO4 addition were carried out using two distinctive sewage sludges as feedstocks. Results showed that KMnO4 addition increased the VFAs yield up to 144 and 196 mgCOD/g VSS for the two sludges. When KMnO4 was used as pre-treatment, 55 % of sCOD were VFAs. This latter result was mainly debited to the recalcitrant organics’ disruption promoted by the oxidative permanganate ability

Thermal hydrolysis pre-treatment has no positive influence on volatile fatty acids production from sewage sludge

The study compares the potential to produce volatile fatty acids (VFA) from sewage sludge, both raw and thermally pre-treated in two modes of operation. In batch mode, raw sludge at pH 8 obtained the highest maximum VFA yield (0.41 g COD-VFA/g CODfed) whereas pre-treated sludge achieved a lower value (0.27 g COD-VFA/g CODfed). The operation of 5-L continuous reactors showed that thermal hydrolysis pre-treatment (THP) did not have any significant influence on VFA yields, averaging 15.1 % g COD-VFA/g COD with raw sludge and 16.6 % g COD-VFA/g COD with pre-treated one. Microbial community analysis showed that phylum Firmicutes was predominant in both reactors and that the enzymatic profiles involved in VFA production were very similar regardless of the substrate fedThis work is part of the ECOVAL and CIGAT CIRCULAR projects, which are funded by Interreg Sudoe (SOE4/P1/E1104) and by the Xunta de Galicia and Viaqua (IN853C2022/03), respectively. Juan M. Lema belongs to the Galician competitive research group ED431C-2021/37 co-funded by Xunta de Galicia and ERDF (EU)S

Biomethane production improvement by enzymatic pretreatments and enhancers of sewage sludge anaerobic digestion

Enzymatic hydrolysis is recognised as an effective pre-treatment for increasing biodegradability of sludge. In this work, isolated commercial enzymes as well as in-situ enzymes producer bacteria were used respectively as enhancers and pre-treatments of sewage sludge. Biodegradability of sample as well as biomethane potential production were studied. Results showed that depuration efficiencies in terms of CODs (73.5-85.5 %) and TVS (28.5-42.7 %) were more than twice the control value. In addition, pre-treated samples as well as enhanced samples with enzymes generated more biomethane than control. The optimal ones, were those with the isolated proteases (P) and with bacteria (Bacillus licheniformis) treatment in-situ (F), producing a total volume of 72.4 ± 2.62 ml CH4 and 114 ml ± 0.46 CH4, respectively, increasing the biogas volume in 3.65 and 5.77 times respectively compared with control