Biomass production from fermented starch wastewater in photo-bioreactor with internal overflow recirculation

Lactic acid wastewater treatment by photosynthetic bacteria and simultaneous production of protein and pigments

Photosynthetic bacteria (PSB) can be used in wastewater treatment to simultaneously remove pollutants and produce valuable biomass. In this study, PSB were used to treat lactic acid wastewater and produce high-value substances (protein, carotenoid and bacteriochlorophyll). The results showed that the PSB biomass increase, COD and NH4+-N removal reached 55%, 89% and 94% in 5 days, respectively. The protein content, carotenoid and bacteriochlorophyll concentrations reached 69.1%, 2.3 and 0.8 mg/L, respectively. Furthermore, kinetic analysis showed that both NH4+-N removal and protein content fitted the Boltzmann equation, and the NH4+-N removal was positively related with the content of protein and concentration of pigments. This novel wastewater treatment method can adapt to the changes of light-oxygen condition, F/M and pH conditions.Highlights(1) PSB effectively treated real lactic acid wastewater with zero excess sludge.(2) 69% of protein and 2.3 mg/L of carotenoid were produced in the process.(3) NH4+-N removal was positively related with the content of protein and pigments.

Purple non-sulfur bacteria technology: a promising and potential approach for wastewater treatment and bioresources recovery

Shortage of water, energy, and bioresources in the world has led to the exploration of new technologies that achieve resource recovery from wastewater, which has become a new sustainable trend. Photosynthetic non-sulfur bacteria (PNSB), the most ancient photo microorganism, not only treats different wastewater types, but also generates PNSB cells, which are non-toxic bioresources and containing many value-added products. These bioresources can be used as raw materials in the agricultural, food, and medical industries. Therefore, PNSB or PNSB-based wastewater resource recovery technology can be simultaneously used to treat wastewater and produce useful bioresources. Compared with traditional wastewater treatment, this technology can reduce CO₂ emissions, promote the N recovery ratio and prevent residual sludge disposal or generation. After being developed for over half a century, PNSB wastewater resource recovery technology is currently extended towards industrial applications. Here, this technology is comprehensively introduced in terms of (1) PNSB characteristics and metabolism; (2) PNSB wastewater treatment and bioresource recovery efficiency; (3) the relative factors influencing the performance of this technology, including light, oxygen, strains, wastewater types, hydraulic retention time, on wastewater treatment, and resource production; (4) PNSB value-added bioresources and their generation from wastewater; (5) the scale-up history of PNSB technology; (6) Finally, the future perspectives and challenges of this technology were also analysed and summarised.

Pilot-Scale Airlift Bioreactor with Function-Enhanced Microbes for the Reduction of Refinery Excess Sludge

A pilot-scale airlift bioreactor (ALBR) system was built and operated continuously for refinery excess sludge (RES) reduction. Combined ALBR and function-enhanced microbes (composed of photosynthetic bacteria and yeast) were integrated into the system. The pilot-scale ALBR was operated for 62 days, and the start-up time was 7 d. Continuous operation showed that the sludge reduction efficiency was more than 56.22%, and the water quality of the effluent was satisfactory. This study focused on investigating the effects of hydraulic retention time (HRT) on the stability of the system and the effect of sludge reduction. Under different HRT conditions of 40, 26.7, 20, and 16 h, the sludge reduction rates reached 56.22%, 73.24%, 74.09%, and 69.64%, respectively. The removal rates of chemical oxygen demand (COD) and total nitrogen (TN) decreased with decreasing HRT, whereas the removal rate of NH₄⁺-N increased. The removal rate of total phosphorus (TP) was approximately 30%. Results indicate that the ALBR and function-enhanced microbe system can reduce sludge and treat sewage simultaneously, and the effluent is up to the national emission standard. Addition of function-enhanced microbes can promote the degradation of petroleum hydrocarbon substances in the sludge, especially alkanes with low carbon numbers. This study suggests that the optimal HRT for the system is 16 h. The total operation cost of the ALBR combined with the function-enhanced microbe system can be reduced by 50% compared with the cost of direct treatment of the RES system.

Protein recovery as a resource from waste specifically via membrane technology-from waste to wonder

Economic growth and the rapid increase in the world population has led to a greater need for natural resources, which in turn, has put pressure on said resources along with the environment. Water, food, and energy, among other resources, pose a huge challenge. Numerous essential resources, including organic substances and valuable nutrients, can be found in wastewater, and these could be recovered with efficient technologies. Protein recovery from waste streams can provide an alternative resource that could be utilized as animal feed. Membrane separation, adsorption, and microbe-assisted protein recovery have been proposed as technologies that could be used for the aforementioned protein recovery. This present study focuses on the applicability of different technologies for protein recovery from different wastewaters. Membrane technology has been proven to be efficient for the effective concentration of proteins from waste sources. The main emphasis of the present short communication is to explore the possible strategies that could be utilized to recover or restore proteins from different wastewater sources. The presented study emphasizes the applicability of the recovery of proteins from various waste sources using membranes and the combination of the membrane process. Future research should focus on novel technologies that can help in the efficient extraction of these high-value compounds from wastes. Lastly, this short communication will evaluate the possibility of integrating membrane technology. This study will discuss the important proteins present in different industrial waste streams, such as those of potatoes, poultry, dairy, seafood and alfalfa, and the possible state of the art technologies for the recovery of these valuable proteins from the wastewater.

Application of purple phototrophic bacteria in a biofilm photobioreactor for single cell protein production: Biofilm vs suspended growth

Single cell protein (SCP), has been proposed as alternative to effectively upgrade and recycle organics and nutrients from wastewater. Biomass recovery is a critical issue, and recovery as a biofilm is effective in comparison with sedimentation of suspended biomass. This study aims to determine the applicability of purple phototrophic bacteria (PPB) biofilm on infra-red irradiated, submerged surfaces for the treatment of pre-settled red meat processing wastewater, and SCP generation. PPB removed up to 66% of COD and 42% of TN and TP during batch operation with total areal productivities between 15 and 20 gVS m^-2 d^-1 achieved. More than 60% of the total biomass grew attached (as biofilm) with the remainder being suspended. The biofilm can be harvested at around 160 gTS L^-1 with high protein (>96 g L^-1) and low ash contents (>4.0% compared to >30% in the wastewater). The compositions of attached and suspended biomass differed significantly, where the suspended fraction resembled the wastewater composition (e.g. in terms of inert components). The PPB community was similar in the suspended and biofilm fractions while the biofilm had higher relative abundance of PPB representatives (57% vs 43%). A consistent product composition is highly relevant for the manufacturer and ultimately determines the value as feed, feed additive, or supplement.

Enhanced removal of veterinary antibiotic from wastewater by photoelectroactive biofilm of purple anoxygenic phototroph through photosynthetic electron uptake

Purple anoxygenic phototrophs have been recently attracted substantial attention for their growing potential in wastewater treatment and their diverse metabolic patterns can be regulated for process control and optimization. In this study, the photoheterotrophic metabolism of Rhodopseudomonas palustris (R. palustris) was modified by photosynthetic electron uptake using a poised electrode which was explored to enhance removal of veterinary antibiotic from aqueous medium. The results showed that R. palustris grown as biofilm on electrode surface had excellent photoelectroactive activity and the photosynthetic electron uptake from the photoelectroactive biofilm significantly enhanced antibiotic florfenicol (FLO) degradation. The specific degradation rate of FLO at the set electrode potential of 0 V was 2.59-fold higher than that without applied potential. Enhanced co-metabolic reductive dehalogenation by use of the photosynthetic electrons extracted from co-substrate was mainly responsible for FLO degradation which eliminated the antibacterial activity of FLO. The electrode potential controlled the processes of photosynthetic electron uptake and its resultant FLO degradation. The fastest degradation of FLO was achieved at 0 V because the electrode poised at this potential stroke a proper balance between the enhancing photosynthetic electron uptake by serving as electron acceptor and minimizing competition with FLO for the photosynthetic electron from co-substrate. The activity of photoelectroactive biofilm was not negatively affected by FLO at environmental relevant concentration, suggesting its great potential for removal of antibiotic contaminants in wastewater. R. palustris could serve as a reservoir for floR resistance gene but its abundance can be diminished by choosing appropriate electrode potential.

Photosynthetic bacteria-based technology is a potential alternative to meet sustainable wastewater treatment requirement?

A paradigm shift is underway in wastewater treatment from pollution removal to resource or energy recovery. However, conventional activated sludge (CAS) as the core technology of wastewater treatment is confronted with severe challenges on high energy consumption, sludge disposal and inevitable greenhouse gas emission, which are posing a serious impact on the current wastewater industry. It is urgent to find new alternative methods to remedy these defects. Photosynthetic bacteria (PSB) have flexible metabolic modes and high tolerance, which enhance the removal of nutrients, heavy metals and organic contaminants efficiency in different wastewater. The unique phototrophic growth of PSB breaks the restriction of nutrient metabolism in the CAS system. Recent studies have shown that PSB-based technologies can not only achieve the recovery of nutrient and energy, but also improve the degradation efficiency of refractory substances. If the application parameters can be determined, there will be great prospects and economic effects. This review summarizes the research breakthroughs and application promotion of PSB-based wastewater treatment technology in recent years. Comparing discussed the superiority and inferiority from the perspective of application range, performance differences and recovery possibility. Pathways involved in the nutrient substance and the corresponding influencing parameters are also described in detail. The mode of PSB biodegradation processes presented a promising alternative for new wastewater treatment scheme. In the future, more mechanical and model studies, deterministic operating parameters, revolutionary process design is need for large-scale industrial promotion of PSB-based wastewater treatment.

Photosynthetic bacteria wastewater treatment with the production of value-added products: A review

Wastewater resource recovery can generate environmental and economic benefits; especially, value-added substance recovery from wastewater can create profits. Photosynthetic bacteria (PSB) can produce protein, coenzyme Q₁₀, 5-ALA, carotenoids, bacteriochlorin, and polyhydroxyalkanoates while treating wastewaters. This review consists of four parts: (1) PSB wastewater treatment, including influence factors and enhancement methods for value-added substances production; (2) downstream processing, including cell separation from effluent, extraction of value-added substances, and purification; (3) comparison among different wastewater resource recovery technologies and brief economic analysis; (4) future development. The focus of this review is the whole procedure of PSB value-added substance production from wastewater. Recent progress of theoretical researches, practical researches and economic issues were systematically summarized and critically analyzed with the scope of promoting PSB technology from concept to practice.

Recycling of sugar industry wastewater for single-cell protein production with supplemental carotenoids

The bioconversion of sugar-industry wastewater to value-added products is a prominent topic in biotechnology. This work cultured a carotenoid-producing photosynthetic bacterium, Rhodopseudomonas faecalis, in a photo-bioreactor containing different wastewater from wastewater treatment ponds of a Thai sugar company. The cultivated R. faecalis produced single cell protein (SCP) with supplemental carotenoids. The cultivation boosted the growth and dehydrogenase activity of R. faecalis from all wastewater sources, while significantly reducing the total sugar concentration. The cellular protein concentration and carotenoid production of R. faecalis was maximised in wastewater collected from anaerobic pond and secondary mechanically aerated pond, respectively. At the end of the cultivation, the chemical oxygen demand was reduced by 80% and the protein content in the dry biomass exceeded 50%, within the acceptable ranges of SCP production. The biomass contained all essential amino acids and the leucine and lysine proportions were above the SCP guideline values. This study reveals that sugar-industry wastewater can be recycled in SCP production with supplemental carotenoids. The SCP is a potential commercial product for the sugar industry.

Effects of light intensity and photoperiod on pigments production and corresponding key gene expression of Rhodopseudomonas palustris in a photobioreactor system

Light intensity and photoperiod significantly affect Rhodopseudomonas palustris growth and pigments production and their optimization is necessary for pigment biosynthesis. In this study, the impacts of different light intensity and light/dark cycles were investigated on biomass, carotenoids, bacteriochlorophyll production, together with pollutant removal, in a photobioreactor system. Results showed that R. palustris had the highest carotenoids and bacteriochlorophyll productions with light intensity of 150 μmol-photons/m²/s and light/dark cycle of 4/2 (16 h/8h). The corresponding values were 1.94 mg/g-biomass and 1.17 mg/g-biomass, respectively. The effects of light/dark cycle on crtA and bchE gene expression in pigments biosynthesis were also studied. Mechanism analysis revealed that carotenoids and bacteriochlorophyll yields represented good synergistic effect, which was consistent with the up-regulation of crtA and bchE gene expressions under optimal light/dark cycle of 4/2.

Bio-conversion of photosynthetic bacteria from non-toxic wastewater to realize wastewater treatment and bioresource recovery: A review

Generating or recycling water and resources from wastewater other than just treating wastewater is one of the most popular trends worldwide. Photosynthetic bacteria (PSB) wastewater treatment and resource recovery technology is one of the most potential methods. PSBs are non-toxic and contain lots of value-added products that can be utilized in the agricultural and food industries. They are effective to degrade pollutants and synthesize useful biomass, thus realizing wastewater treatment, bioresource production, and eliminating waste sludge. If all the nutrients in wastewaters could be bio-converted by PSB, then pollutant reductions and economic benefits would be achieved. This review paper firstly describes and summarizes this technology, including PSBs classification, metabolism, and the market application. The feasibility, technical procedures, bioreactors, pollutant removal, and bioresource production are also summarized, compared and evaluated. Issues that concern the advantages and industrialization of this technologies at the plant scale are also discussed.

Brewery wastewater treatment and resource recovery through long term continuous-mode operation in pilot photosynthetic bacteria-membrane bioreactor

Photosynthetic bacteria (PSB) are considered ideal for high COD wastewater treatment and resource recovery. This work is the first continuous-mode long-term (440 days) pilot study (240 L) by using PSB-membrane (PSB-MBR) system for such purpose. Results showed that the system started-up in 27 days for brewery wastewater and then stably operated under various temperature, initial COD and pH conditions, which showed fast start-up and strong robustness. Comparing with small-batch PSB-MBR system, the capacity of pollutants treatment degradation rate in the pilot-continuous PSB-MBR system was promoted. The operation parameters for pilot-continuous PSB-MBR system were determined as follows: light-micro aerobic, 72 h hydraulic retention time, 1200 mg L^-1 inoculum size and 1.0 g L^-1 d^-1 organic loading rate, 2.5 F/M. Under these conditions, the COD and NH₄⁺ in effluent were below 80 and 15 mg L^-1, respectively. The PSB cell production reached 483.5 mg L^-1 d^-1 with protein, polysaccharides, carotenoid, bacteriochlorophyll, and coenzyme Q10 of 420.9, 177.6, 2.53, 10.75, 38.6 mg g^-1, respectively, showing great potential of resource recovery from organic wastewater. In addition, the collected biomass had no acute toxicity to crucian carps. This work provides a base for the scale-up of this novel technology.

Simultaneous treatment and single cell protein production from agri-industrial wastewaters using purple phototrophic bacteria or microalgae - A comparison

Resource recovery, preferably as high value products, is becoming an integral part of modern wastewater treatment, with conversion to heterotrophic or phototrophic/photosynthetic microbes a key option to minimise dissipation, and maximise recovery. This study compares the treatment capacities of purple phototrophic bacteria (PPB) and microalgae of five agri-industrial wastewaters (pork, poultry, red meat, dairy and sugar) to recover carbon, nitrogen, and phosphorous as a microbial product. The mediators have different advantages, with PPB offering moderate removals (up to 74% COD, 80% NH₄-N, 55% PO₄-P) but higher yields (>0.75 gCOD_removed gCOD_added^-1) and a more consistent, PPB dominated (>50%) product, with a higher crude protein product (>0.6 gCP gVSS^-1). The microalgae tests achieved a better removal outcome (up to 91%COD, 91% NH₄-N, 73%PO₄-P), but with poorer quality product, and <30% abundance as algae.

One-step treatment and resource recovery of high-concentration non-toxic organic wastewater by photosynthetic bacteria

In order to achieve simple pollutant removal and simultaneous resource recovery in high-COD-non-toxic wastewater treatment, a one-step photosynthetic bacteria (PSB) method was established using batch study experiment. The effluent COD met the national discharge standard, and biomass with rich protein and high-value substances was efficiently produced. It eliminated the demand of post-treatment for conventional PSB treatment. Results showed that Rhodopseudomonas effectively treated brewery wastewater and achieved biomass proliferation. Yeast extract was the best additive for PSB growth and the effluent COD was below 80 mg/L with 400 mg/L yeast extract, meeting the national discharge standard. In addition, the PSB biomass increased by 2.6 times, and the cells were rich in protein, polysaccharide, carotenoids, bacteriochlorophyll and coenzyme Q10, reaching 420.9, 177.6, 2.53, 10.75 and 38.6 mg/g respectively. This work demonstrated the great potential of PSB for high-COD non-toxic wastewater treatment in one-step process.

Variation of the characteristics of biofilm on the semi-suspended bio-carrier produced by a 3D printing technique: Investigation of a whole growing cycle

The presented investigation focused on exploring the characteristics of the biofilm formed on a novel semi-suspended bio-carrier and revealing their variation during the whole growing cycle. This used semi-suspended bio-carrier was designed to be a spindle shape, and then fabricated by using a 3D printing technique. Results indicated the bio-carrier provided a suitable environment for the attachment of diverse microorganisms. During the experimental period lasted for 45days, the biofilm quickly attached on the surface of the bio-carrier and grew to maturity, but its characteristics, including the chemical compositions, adhesion force, surface roughness, structure of microbial communities, varied continuously along with the operational time, which greatly influenced the performance of the bioreactor. The shape and structure of bio-carrier, and the shearing force caused by the aeration are important factors that influence the microbial community and its structure, and also heavily affect the formation and growth of biofilm.

The exploration of monochromatic near-infrared LED improved anoxygenic photosynthetic bacteria Rhodopseudomonas sp. for wastewater treatment

The future wastewater treatment requires high-efficiency and energy-saving technology. Anoxygenic photosynthetic bacteria (APB) is deemed as an eco-friendly microorganism, which could be employed in wastewater treatment. Here, monochromatic near-infrared (MNIR) light emitting diode (LED) was used, and three key factors (light quality, light intensity and photoperiod) of it were analyzed by a response surface methodology (RSM) in APB wastewater treatment. The results showed that light quality was the biggest impact factor in APB wastewater treatment, and nearly 58.07% of NH₄⁺-N and 70.62% of chemical oxygen demand (COD) could be removed based on 46.4% of that theoretically possible. The light quality's study revealed that APB had the highest NH₄⁺-N and COD removal, biomass production, and bacteriochlorophyll a production with 850nm IR LED. Moreover, the application of optimal MNIR LED could not only save energy, but also avoid algae bloom of photo-bioreactors (PBR).

Treatment of anaerobically digested swine wastewater by Rhodobacter blasticus and Rhodobacter capsulatus

Two strains of photosynthetic bacteria, Rhodobacter blasticus and Rhodobacter capsulatus, were used in this work to investigate the feasibility of using photosynthetic bacteria for the treatment of anaerobically digested swine wastewater. The effects of crucial factors which influence the pollutants removal efficiency were also examined. Results showed that anaerobically digested swine wastewater could be treated effectively by photosynthetic bacteria. The treatment efficiency was significantly higher by the mixed photosynthetic bacteria than that by any unitary bacterium. The optimal treatment condition by mixed bacteria was inoculation of 10.0%(v/v) of the two bacteria by 1:1, initial pH of 7.0 and initial chemical oxygen demand of 4800mgL^-1. Under these conditions, the removal rate of chemical oxygen demand was 83.3%, which was 19.3% higher than when using Rhodobacter blasticus or 10.6% higher than when using Rhodobacter capsulatus separately. This mixed photosynthetic bacteria achieved high chemical oxygen demand removal and cell yields.

Performance, 5-aminolevulinic acid (ALA) yield and microbial population dynamics in a photobioreactor system treating soybean wastewater: Effect of hydraulic retention time (HRT) and organic loading rate (OLR)

Effects of hydraulic retention time (HRT) and influent organic loading rate (OLR) were investigated in a photobioreactor containing PNSB (Rhodobacter sphaeroides)-chemoheterotrophic bacteria to treat soybean wastewater. Pollutants removal, biomass production and ALA yield in different phases were investigated in together with functional microbial population dynamics. The results showed that proper HRT and OLR increased the photobioreactor performance including pollutants removal, biomass and ALA productions. 89.5% COD, 90.6% TN and 91.2% TP removals were achieved as well as the highest biomass production of 2655mg/L and ALA yield of 7.40mg/g-biomass under the optimal HRT of 60h and OLR of 2.48g/L/d. In addition, HRT and OLR have important impacts on PNSB and total bacteria dynamics.

Performance, carotenoids yield and microbial population dynamics in a photobioreactor system treating acidic wastewater: Effect of hydraulic retention time (HRT) and organic loading rate (OLR)

Effects of hydraulic retention time (HRT) and influent organic loading rate (OLR) were investigated in a photobioreactor containing PNSB (Rhodopseudomonas palustris)-chemoheterotrophic bacteria to treat volatile fatty acid wastewater. Pollutants removal, biomass production and carotenoids yield in different phases were investigated in together with functional microbial population dynamics. The results indicated that properly decreasing HRT and increasing OLR improved the nutrient removal performance as well as the biomass and carotenoids productions. 85.7% COD, 89.9% TN and 91.8% TP removals were achieved under the optimal HRT of 48h and OLR of 2.51g/L/d. Meanwhile, the highest biomass production and carotenoids yield were 2719.3mg/L and 3.91mg/g-biomass respectively. In addition, HRT and OLR have obvious impacts on PNSB and total bacteria dynamics. Statistical analyses indicated that the COD removal exhibited a positive relationship with OLR, biomass and carotenoids production. PNSB/total bacteria ratio had a positive correlation with the carotenoids yield.

Improved biomass production by humic analog anthraquinone-2-sulfonate from kitchen waste in a two-phase system

The volatile fatty acids from kitchen waste were used as substrates of anoxygenic photosynthetic bacteria (APB) in a dark-photo fermentation reactor, and anthraquinone-2-sulfonate (AQS) was firstly applied to boost the biomass yield.

Biomass and pigments production in photosynthetic bacteria wastewater treatment: Effects of photoperiod

This study aimed at enhancing the bacterial biomass and pigments production in together with pollution removal in photosynthetic bacteria (PSB) wastewater treatment via using different photoperiods. Different light/dark cycles and light/dark cycle frequencies were examined. Results showed that PSB had the highest biomass production, COD removal and biomass yield, and light energy efficiency with light/dark cycle of 2h/1h. The corresponding biomass, COD removal and biomass yield reached 2068mg/L, 90.3%, and 0.38mg-biomass/mg-COD-removal, respectively. PSB showed higher biomass production and biomass yield with higher light/dark cycle frequency. Mechanism analysis showed within a light/dark cycle from 1h/2h to 2h/1h, the carotenoid and bacteriochlorophyll production increased with an increase in light/dark cycle. Moreover, the pigment contents were much higher with lower frequency of 2-4 times/d.

A multiphase mixture model for substrate concentration distribution characteristics and photo-hydrogen production performance of the entrapped-cell photobioreactor

A multiphase mixture model was developed for revealing the interaction mechanism between biochemical reactions and transfer processes in the entrapped-cell photobioreactor packed with gel granules containing Rhodopseudomonas palustris CQK 01. The effects of difference operation parameters, including operation temperature, influent medium pH value and porosity of packed bed, on substrate concentration distribution characteristics and photo-hydrogen production performance were investigated. The results showed that the model predictions were in good agreement with the experimental data reported. Moreover, the operation temperature of 30 °C and the influent medium pH value of 7 were the most suitable conditions for photo-hydrogen production by biodegrading substrate. In addition, the lower porosity of packed bed was beneficial to enhance photo-hydrogen production performance owing to the improvement on the amount of substrate transferred into gel granules caused by the increased specific area for substrate transfer in the elemental volume.

Biomass and pigments production in photosynthetic bacteria wastewater treatment: effects of light sources

This study is aimed at enhancing biomass and pigments production together with pollution removal in photosynthetic bacteria (PSB) wastewater treatment via different light sources. Red, yellow, blue, white LED and incandescent lamp were used. Results showed different light sources had great effects on the PSB. PSB had the highest biomass production, COD removal and biomass yield with red LED. The corresponding biomass, COD removal and biomass yield reached 2580 mg/L, 88.6% and 0.49 mg-biomass/mg-COD-removal, respectively. The hydraulic retention time of wastewater treatment could be shortened to 72 h with red LED. Mechanism analysis showed higher ATP was produced with red LED than others. Light sources could significantly affect the pigments production. The pigments productions were greatly higher with LED than incandescent lamp. Yellow LED had the highest pigments production while red LED produced the highest carotenoid/bacteriochlorophyll ratio. Considering both efficiency and energy cost, red LED was the optimal light source.