Fan Meng

Denitrification of aging biogas slurry from livestock farm by photosynthetic bacteria

Huge amount of aging biogas slurry is in urgent need to be treated properly. However, due to high NH3-N concentration and low C/N ratio, this aging biogas slurry is refractory for traditional methods. Its denitrification has become a big challenge. In this paper, photosynthetic bacteria (PSB) were employed to handle this problem. The results showed denitrification of aging biogas slurry by PSB treatment was promising. The highest removal efficiency of NH3-N reached 99.75%, much higher than all other treatments. The removal of NH3-N followed pseudo zero order reaction under dark-aerobic condition. The better inoculation rate for NH3-N removal was 30%; and aerobic condition was more beneficial for NH3-N removal than anaerobic condition because of different metabolic pathways.

Effects of dissolved oxygen concentration on photosynthetic bacteria wastewater treatment: Pollutants removal, cell growth and pigments production

Dissolved oxygen (DO) is an important parameter in photosynthetic bacteria (PSB) wastewater treatment. This study set different DO levels and detected the pollutants removal, PSB growth and pigments production. Results showed that DO significantly influenced the performances of PSB wastewater treatment process. The highest COD (93%) and NH3-N removal (83%) was achieved under DO of 4-8mg/L, but DO of 2-4mg/L was recommended considering the aeration cost. PSB biomass reached 1645mg/L under DO of 4-8mg/L with satisfying co-enzyme Q10 content. The biomass yield was relatively stable at all DO levels. For bacteriochlorophyll and carotenoids, DO>1mg/L could satisfy their production. On the other hand, DO<0.5mg/L led to the highest dehydrogenase activity. According to the different purposes, the optimal treatment time was different. The most pigments production occurred at 24h; biomass reached peak at 48h; and the optimal time for pollutants removal was 72h.

Enhancing protein to extremely high content in photosynthetic bacteria during biogas slurry treatment

This work proposed a novel approach to achieve an extremely high protein content in photosynthetic bacteria (PSB) using biogas slurry as a culturing medium. The results showed the protein content of PSB could be enhanced strongly to 90% in the biogas slurry, which was much higher than reported microbial protein contents. The slurry was partially purified at the same time. Dark-aerobic was more beneficial than light-anaerobic condition for protein accumulation. High salinity and high ammonia of the biogas slurry were the main causes for protein enhancement. In addition, the biogas slurry provided a good buffer system for PSB to grow. The biosynthesis mechanism of protein in PSB was explored according to theoretical analysis. During biogas slurry treatment, the activities of glutamate synthase and glutamine synthetase were increased by 26.55%, 46.95% respectively.

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.

Membrane concentrate treatment by photosynthetic bacteria: Feasibility and tolerance mechanism analysis

Refractory membrane concentrate generated from the membrane bioreactor (MBR) process remains a big challenge. With high pollution loads, high salinity and low biodegradability, membrane concentrates are difficult to be treated by conventional biological treatments. In this work, photosynthetic bacteria (PSB) were employed to handle this problem. The results showed that PSB could simultaneously remove COD, NH3-N, NO3--N, salinity and chroma from the membrane concentrate. The removal efficiency of COD, NH3-N, NO3--N, salinity and chroma reached 24.0%, 78.0%, 81.6%, 57.0% and 60.0% respectively. Dark-aerobic condition was more beneficial for pollutants removal. The tolerance mechanism of PSB in treating membrane concentrate was then analyzed. The contents of protein and carotenoid in PSB increased by 38.7% and 20.7% due to the defense stress effects. The content of bacteriochlorin decreased by 42.9% while the content of coenzyme Q10 was stable at 8.4-8.8%.

A special light-aerobic condition for photosynthetic bacteria-membrane bioreactor technology

The combined photosynthetic bacteria (PSB) and membrane bioreactor (MBR) technology has the great advantage of simultaneously realizing wastewater purification and bio-resource recovery and has attracted increasing attention in recent years. Light-oxygen conditions are the most vital factor in wastewater treatment. The special light-aerobic condition was first applied to PSB-MBR wastewater treatment, and it was compared with three typical light-oxygen conditions. The results showed that the highest chemical oxygen demand (COD) removal efficiency (96.28%) and the highest biomass production (1.12 g/L/d) were simultaneously obtained under light-aerobic condition. This phenomenon overcame the limitations whereby optimal pollutant removal and bio-resource recovery could not be achieved at the same time. An analysis of the microbial community showed that different light-oxygen conditions caused large variations in the microbial community composition of PSB-MBR. The microbial diversity was lower when light and oxygen co-existed.