A systematic optimization of piggery wastewater treatment with purple phototrophic bacteria

Potential of enriched phototrophic purple bacteria for H2 bioconversion into single cell protein

Single cell protein (SCP) has emerged as an alternative protein source, potentially based on the recovery of carbon and nutrients from waste-derived resources as part of the circular economy. From those resources, gaseous substrates have the advantage of an easy sterilization, allowing the production of pathogen-free SCP. Sterile gaseous substrates allow producing pathogen-free SCP. This study evaluated the use of an enriched phototrophic purple bacteria (PPB) consortium for SCP production using H2 and CO2 as electron and C sources. The influence of pH (6.0-8.5), temperature (15-50 °C) and light intensity (0-50 W·m-2) on the growth kinetics and biomass yields was investigated using batch tests. Optimal conditions were found at pH 7, 25 °C and light intensities over 30 W·m-2. High biomass and protein yields were achieved (~ 1 g CODbiomass·g CODH2consumed-1 and 3.9-4.4 g protein·g H2-1) regardless of the environmental conditions, being amongst the highest values reported from gaseous streams. These high yields were obtained thanks to the use of light as a sole energy source by the PPB consortium, allowing a total utilization of H2 for growth. Hydrogen uptake rates varied considerably, with values up to 61 ± 5 mg COD·d-1 for the overall H2 consumption rates and 2.00 ± 0.14 g COD·g COD-1·d-1 for the maximum specific uptake rates under optimal growth conditions. The latter value was estimated using a mechanistic model able to represent PPB growth on H2. The biomass exhibited high protein contents (>50 % w/w) and adequate amino acid profiles, showing its suitability as SCP for feed. PPB were the dominant bacteria during the experiments (relative abundance over 80 % in most tests), with a stable population dominated by Rhodobacter sp. and Rhodopseudomonas sp. This study demonstrates the potential of enriched PPB cultures for H2 bioconversion into SCP.

The potential and sustainable strategy for swine wastewater treatment: Resource recovery

Swine wastewater is highly polluted with complex and harmful substances that require effective treatment to minimize environmental damage. There are three commonly used biological technologies for treating swine wastewater: conventional biological technology (CBT), microbial electrochemical technology (MET), and microalgae technology (MT). However, there is a lack of comparison among these technologies and a lack of understanding of their unique advantages and efficient operation strategies. This review aims to compare and contrast the characteristics, influencing factors, improvement methods, and microbial mechanisms of each technology. CBT is cost-effective but has low resource recovery efficiency, while MET and MT have the highest potential for resource recovery. However, all three technologies are affected by various factors and toxic substances such as heavy metals and antibiotics. Improved methods include exogenous/endogenous enhancement, series reactor operation, algal-bacterial symbiosis system construction, etc. Though MET is limited by construction costs, CBT and MT have practical applications. While swine wastewater treatment processes have developed automatic control systems, the application need further promotion. Furthermore, key functional microorganisms involved in CBT's pollutant removal or transformation have been detected, as have related genes. The unique electroactive microbial cooperation mode and symbiotic mode of MET and MT were also revealed, respectively. Importantly, the future research should focus on broadening the scope and scale of engineering applications, preventing and controlling emerging pollutants, improving automated management level, focusing on microbial synergistic metabolism, enhancing resource recovery performance, and building a circular economy based on low-cost and resource utilization.

Photoautotrophic removal of hydrogen sulfide from biogas using purple and green sulfur bacteria

Biogas desulfurization based on anoxygenic photosynthetic processes represents an alternative to physicochemical technologies, decreasing the risk of O₂ and N₂ contamination. This work aimed at assessing the potential of Allochromatium vinosum and Chlorobium limicola for biogas desulfurization under different light intensities (10 and 25 klx) and H₂S concentrations (1 %, 1.5 % and 2 %) in batch photobioreactors. In addition, the influence of rising biogas flow rates (2.9, 5.8 and 11.5 L d^-1 in stage I, II and III, respectively) on the desulfurization performance in a 2.3 L photobioreactor utilizing C. limicola under continuous mode was assessed. The light intensity of 25 klx negatively influenced the growth of A. vinosum and C. limicola, resulting in decreased H₂S removal capacity. An increase in H₂S concentrations resulted in higher volumetric H₂S removal rates in C. limicola (2.9-5.3 mg L^-1 d^-1) tests compared to A. vinosum (2.4-4.6 mg L^-1 d^-1) tests. The continuous photobioreactor completely removed H₂S from biogas in stage I and II. The highest flow rate in stage III induced a deterioration in the desulfurization activity of C. limicola. Overall, the high H₂S tolerance of A. vinosum and C. limicola supports their use in H₂S desulfurization from biogas.

Nitrogen recovery from wastewater by microbial assimilation - A review

The increased nitrogen (N) input with low utilization rate in artificial N management has led to massive reactive N (Nr) flows, putting the Earth in a high-risk state. It is essential to recover and recycle Nr during or after Nr removal from wastewater to reduce N input while simultaneously mitigate Nr pollution in addressing the N stress. However, mechanisms for efficient Nr recovery during or after Nr removal remain unclear. Here, the occurrence of N risk and progress in wastewater treatment in recent years as well as challenges of the current technologies for N recovery from wastewater were reviewed. Through analyzing N conversion fluxes in biogeochemical N-cycling networks, microbial N assimilation through photosynthetic and heterotrophic microorganisms was highlighted as promising alternative for synergistic N removal and recovery in wastewater treatment. In addition, the prospects and gaps of Nr recovery from wastewater through microbial assimilation are discussed.

Periodic oxygen supplementation drives efficient metabolism for enhancing valuable bioresource production in photosynthetic bacteria wastewater treatment

Periodic oxygen supplementation (A-O) strategy was proposed to improve pollutant removal and enhance bioresource production of photosynthetic bacteria (PSB). The A-O strategy obtained higher COD (91.4%) and NH₄⁺-N (78.6%) removal compared with the non-oxygen supplementation (N-O) strategy, which was similar to the continuous oxygen supplementation (C-O) strategy. A-O strategy achieved the highest biomass concentration of 1338.5 mg/L. Bacteriochlorophyll and carotenoids concentration in the A-O strategy were 24.9-31.1% and 15.1-23.7% higher than those in the other two strategies; coenzyme Q₁₀ concentration and content were 52.5% and 21.3% higher than that in the N-O strategy. The metabolomic analysis showed that the A-O strategy enhanced the tricarboxylic acid cycle after fumaric acid formation and β-alanine metabolism, then caused higher biomass accumulation. The A-O strategy reduced the inhibition of photophosphorylation by oxidative-phosphorylation and maintained both characteristics. Hence, A-O might be an economic strategy for enhancing pollutant removal and bioresource production in PSB-based wastewater treatment.

N-Doped Biochar as a New Metal-Free Activator of Peroxymonosulfate for Singlet Oxygen-Dominated Catalytic Degradation of Acid Orange 7

In this paper, using rice straw as a raw material and urea as a nitrogen precursor, a composite catalyst (a nitrogen-doped rice straw biochar at the pyrolysis temperature of 800 °C, recorded as NRSBC800) was synthesized by one-step pyrolysis. NRSBC800 was then characterized using XPS, BET, TEM and other technologies, and its catalytic performance as an activator for permonosulfate (PMS) to degrade acid orange 7 (AO7) was studied. The results show that the introduction of N-doping significantly improved the catalytic performance of NRSBC800. The NRSBC800/PMS oxidation system could fully degrade AO7 within 30 min, with the reaction rate constant (2.1 × 10 ^-1 min^-1) being 38 times that of RSBC800 (5.5 × 10^-3 min^-1). Moreover, NRSBC800 not only had better catalytic performance than traditional metal oxides (Co₃O₄ and Fe₃O₄) and carbon nanomaterial (CNT) but also received less impact from environmental water factors (such as anions and humic acids) during the catalytic degradation process. In addition, a quenching test and electron paramagnetic resonance (EPR) research both indicated that AO7 degradation relied mainly on non-free radical oxidation (primarily singlet oxygen (¹O₂)). A recycling experiment further demonstrated NRSBC800's high stability after recycling three times.

Evaluation of Synergies of a Biomass Power Plant and a Biogas Station with a Carbon Capture System

The global carbon emissions from the tertiary sector have increased during the last years, becoming a target sector for carbon capture technologies. This study analyzes the potential application of a carbon capture system (CCS) to the usage of biogas from a livestock waste treatment plant (LWTP) and solid biomass. The proposed BECCS system fulfils the requirement of energy demands of the LWTP and generates electricity. The CCS is sized to consume the biogas produced and the selected operation parameters ensure a high capture efficiency. The BECCS is completed by a Rankine cycle fed by solid biomass and waste heat from the capture process is sized and implemented to produce electricity and steam. The proposed concept handles 1534 kW of solid biomass and 1398 kW of biogas to produce 746.20 kWe and cover the heat demand of a LWTP, 597 kWth. The avoided CO2 emissions sum up to 1620 ton CO2/year. The economic calculations show the limitation of this concept deployment under current prices of electricity and CO2 allowances. Results show the potential feasibility under future scenarios with 5 to 6 payback periods whenever public policies support the use of CCS and EU ETS evolves towards higher prices of carbon allowances.

Stepwise treatment of undiluted raw piggery wastewater, using three microalgal species adapted to high ammonia

A high ammonia concentration and chemical oxygen demand (COD) in piggery wastewater force it to be diluted before conventional microalgal treatment to reduce ammonia toxicity. Incomplete treatment of ammonia and COD in piggery wastewater may cause eutrophication, resulting in algal blooms. This study tried to treat raw piggery wastewater without dilution, using three strains of microalgae (Chlorella sorokiniana, Coelastrella sp. and Acutodesmus nygaardii) that outcompeted other algae under heterotrophic, mixotrophic, and autotrophic conditions, respectively, through adaptive evolution at high ammonia concentration. The three stepwise processes were designed to remove (1) small particles, COD, and phosphorus in the 1st heterotrophic C. sorokiniana cultivation, (2) ammonia and COD in the 2nd mixotrophic Coelastrella sp. cultivation, and (3) the remaining ammonia in the 3rd photoautotrophic A. nygaardii cultivation. To enhance ammonia uptake rate, each algal species were inoculated after 2-day nitrogen starvation. When the N-starved three species were inoculated at each step sequentially at 7 g/L for 2 days, the final phosphorus, COD, and ammonia removal efficiencies were 100% (16.4-0 mg/L), 92% (6820-545 mg/L), 90% (850-81 mg/L) and turbidity (99%) after total 6 days.