Guangming Zhang

Biomass and carotenoid production in photosynthetic bacteria wastewater treatment: effects of light intensity.

This study investigated the feasibility of using photosynthetic bacteria (PSB) to produce biomass and carotenoid while treating wastewater. The effects of light intensity on the biomass, carotenoid and bacteriochlorophyll accumulation in together with pollutant removal were studied. Results showed that it was feasible to use PSB to treat wastewater as well as to produce biomass or carotenoid. 2000 lux was an optimal intensity for biomass production and COD removal, and the corresponding values were 2645 mg/L and 94.7%. 8000 lux was an optimal light intensity for carotenoid production (1.455 mg/L). Mechanism analysis displayed that the greater the bacteriochlorophyll and carotenoid were secreted, the lower the light conversion efficiency turned out to be. The highest light conversion efficiency was achieved at 500 lux; the ATP production, biomass production, and COD removal were the highest at 2000 lux, but the bacteriochlorophyll and carotenoid content were the lowest at 2000 lux.

Degradation properties of protein and carbohydrate during sludge anaerobic digestion

Degradation of protein and carbohydrate is vital for sludge anaerobic digestion performance. However, few studies focused on degradation properties of protein and carbohydrate. This study investigated detailed degradation properties of sludge protein and carbohydrate in order to gain insight into organics removal during anaerobic digestion. Results showed that carbohydrate was more efficiently degraded than protein and was degraded prior to protein. The final removal efficiencies of carbohydrate and protein were 49.7% and 32.2%, respectively. The first 3 days were a lag phase for protein degradation since rapid carbohydrate degradation in this phase led to repression of protease formation. Kinetics results showed that, after initial lag phase, protein degradation followed the first-order kinetic with rate constants of 0.0197 and 0.0018 d(-1) during later rapid degradation phase and slow degradation phase, respectively. Carbohydrate degradation also followed the first-order kinetics with a rate constant of 0.007 d(-1) after initial quick degradation phase.

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.

Sewage sludge disintegration by combined treatment of alkaline+high pressure homogenization.

Alkaline pretreatment combined with high pressure homogenization (HPH) was applied to promote sewage sludge disintegration. For sewage sludge with a total solid content of 1.82%, sludge disintegration degree (DD(COD)) with combined treatment was higher than the sum of DD(COD) with single alkaline and single HPH treatment. NaOH dosage ⩽0.04mol/L, homogenization pressure ⩽60MPa and a single homogenization cycle were the suitable conditions for combined sludge treatment. The combined sludge treatment showed a maximum DD(COD) of 59.26%. By regression analysis, the combined sludge disintegration model was established as 11-DD(COD)=0.713C(0.334)P(0.234)N(0.119), showing that the effect of operating parameters on sludge disintegration followed the order: NaOH dosage>homogenization pressure>number of homogenization cycle. The energy efficiency with combined sludge treatment significantly increased compared with that with single HPH treatment, and the high energy efficiency was achieved at low homogenization pressure with a single homogenization cycle.

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.

High-pressure homogenization pretreatment of four different lignocellulosic biomass for enhancing enzymatic digestibility.

Grass clipping, corn straw, catalpa sawdust and pine sawdust were pretreated with high-pressure homogenization (HPH) to enhance the enzymatic digestibility. With a working pressure of 10 MPa, all the four lignocellulosic biomass were significantly changed, such as decrease in particle size, structure destruction, and crystallinity change. Results showed that lignocellulosic biomass pretreated with HPH yielded more reducing sugar, which was suitable for subsequent biofuel production. After 48-h enzymatic hydrolysis, the maximum reducing sugar yield of 229.42 mg/g was achieved for grass clipping. For corn straw, the enzymatic hydrolysis efficiency increased by 68.37% at most. However, reducing sugar yield of catalpa sawdust and pine sawdust was relatively lower. Low lignin content and crystallinity might make grass clipping the most suitable material for HPH pretreatment, thus leading to high hydrolysis efficiency. HPH pretreatment could increase biofuel output in a mild condition without adding any chemicals.

Enhancement of cell production in photosynthetic bacteria wastewater treatment by low-strength ultrasound.

The present study is aimed at enhanced cell production in together with pollution removal in photosynthetic bacteria wastewater treatment through low-strength ultrasound stimulation. The ultrasound strength was 0.3W/cm(2) with 40kHz frequency. Results showed 1-10min sonication significantly improved the cell production. The optimal sonication time was 2min. When the irradiation period was over 10min, a strong mechanical damage occurred. These phenomena could be explained by the changes of PSB dehydrogenase activity. Sonication stimulated the initial dehydrogenase activity; moderate sonication increased the cell activity while too-long sonication led to quick enzyme activity decrease. The optimal sonication strategy was 1min at the 0th hour and 1min at the 27th hour. The corresponding cell production and cell yield increased by 110% and 93% respectively, and the COD removal reached 98%. The cost of low-strength ultrasound was only 1% of the incremental sales value of cells.

Anaerobic digestion of corn stovers for methane production in a novel bionic reactor.

To improve the biogas production from corn stovers, a new bionic reactor was designed and constructed. The bionic reactor simulated the rumen digestion of ruminants. The liquid was separated from corn stovers and refluxed into corn stovers again, which simulated the undigested particles separated from completely digested materials and fed back again for further degradation in ruminant stomach. Results showed that the bionic reactor was effective for anaerobic digestion of corn stovers. The liquid amount and its reflux showed an obvious positive correlation with biogas production. The highest biogas production rate was 21.6 ml/gVS-addedd, and the total cumulative biogas production was 256.5 ml/gVS-added. The methane content in biogas ranged from 52.2% to 63.3%. The degradation of corn stovers were greatly enhanced through simulating the animal digestion mechanisms in this bionic reactor.