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Algal biofuel has become an attractive alternative of petroleum-based fuels in the past decade. Microalgae have been proposed as a feedstock to produce biodiesel, since they are capable of mitigating CO2 emission and accumulating lipids with high productivity. This article is an overview of the updated status of biofuels, especially biodiesel production from microalgae including fundamental research, culture selection and engineering process development; it summarizes research on mathematical and life cycle modeling on algae growth and biomass production; and it updates global efforts of research and development and commercialization attempts. The major challenges are also discussed. [ABSTRACT FROM AUTHOR]

Cultivating microalgae using municipal wastewater can treat wastewater and recover algal biofuel as an energy source. Wastewater provides necessary nutrients such as nitrogen, phosphorus, and water for microalgal growth. Due to the complexity of the components of municipal wastewater and the complex symbiotic and antagonistic relationship between microalgae and bacteria, it is necessary to select the suitable dominant bacterial species that can promote the microalgae to achieve high lipid production and algal biofuel production using municipal wastewater. Based on the microalgal growth and lipid production, we selected Photosynthetic bacteria and W4 bacteria from 13 different types of bacteria and analyzed the microbial community structure of the municipal wastewater at the end of the microalgal culture cycle. Laboratory test results showed that the amount of lipid production by Photosynthetic bacteria and W4 was 0.114 g·L -1 and 0.113 g·L -1 , which is 22.58% and 21.50% higher than the production by the control group, respectively. According to the gas chromatography (GC) analysis of the lipids, Photosynthetic bacteria and W4 bacteria exerted a relatively low influence on the composition of fatty acids of Chlorella pyrenoidosa but increased the content of monounsaturated fatty acids that improve the grade of biodiesel. The results of the analysis of microbial community structure of the municipal wastewater showed that Photosynthetic and W4 bacteria reduced the richness and diversity of bacterial communities and have the potential to become the dominant bacterial community.

Cultivating microalgae using municipal wastewater can achieve not only treatment of the wastewater but also recovery of algae for use as a biofuel energy source. Wastewater provides necessary nutrients, such as nitrogen and phosphorus, and water for microalgal growth. Because of the complexity of components of municipal wastewater, variety of adaptability, and tolerance to wastewater of different microalgal species, it is necessary to select a suitable microalgal species with high performance in lipid production and identify proper pretreatment of the wastewater to achieve high lipid production using municipal wastewater for algal biofuel production. Based on microalgal growth, lipid production, and clean-up performance of wastewater, we selected Scenedesmus obliquus wild strain and Chlorella pyrenoidosa mutant by ion beam implantation from a test group for the biofuel production. Laboratory test results showed that S. obliquus wild strain and C. pyrenoidosa mutant had respective lipid productions of 0.43 g·L -1 and 0.33 g·L -1 , with more C16-C18 fatty acids, which were suitable for biodiesel production. The pollutant removals from the wastewater by S. obliquus wild strain and C. pyrenoidosa mutant were COD, 86.4% vs. 81.8%; NH 4 + -N, 100.0% vs. 100.0%; TN, 94.3% vs. 94.9%; and TP, 93.4% vs. 94.2% respectively. The two different microalgal strains required different pretreatments. After removal of large particles, the raw wastewater could be directly used for the cultivation of S. obliquus wild strain. To grow C. pyrenoidosa mutant with municipal wastewater, pretreatment procedures including precipitation followed by filtration should be employed.

Harvesting of microalgae is the major challenge in cost-efficient large-scale microalgal biomass production due to their low concentration and small cell size in the culture medium. The present paper aimed to study the efficiency of the filamentous fungus Mucor circinelloides spores suspensions to harvest the green unicellular microalga Chlorella pyrenoidosa grown in synthetic medium. Results showed that the optimal co-culture conditions were pH=6.0, 1.25 g·L -1 glucose and 1:250 fungi to microalgae ratio with harvest efficiency of 91.08%. In addition, the mentioned optimal conditions could be applied for actual sewage with harvest efficiency of 92.33%. Polysaccharide concentrations measured before and after 48 h of cultivation showed that the polysaccharide of C. pyrenoidosa cultured alone was increased by 0.047 g·L -1 , while co-cultured mixture showed increase in polysaccharides by 0.019 g·L -1 . The recorded decrease in polysaccharides concentration in the co-culture might be attributed to using of excreted polysaccharides by M. circinelloides to grow, confirming the symbiotic association of both organisms. Furthermore, with decreasing the pH, C. pyrenoidosa Zeta potential was stable, while it was increased from -37.7 mV to -9.87 mV in M. circinelloides, which indicated that charge neutralization was the mechanism of flocculation between algae and fungi.

A new remediation method for petroleum-salt contaminated soil was proposed, in which wheat straw was applied to enhance salt leaching and meanwhile block salt upmovement along the soil capillary. It was shown that the existence of petroleum increased the surface hydrophobicity of soil and thus hindered the leaching process once the oil content was above 1.5% (mass fraction). The application of 5% (mass fraction) wheat straw into the soil increased the efficiency of salt leaching from 3% to 25%. The effectiveness of wheat straw layer in inhibiting the salt upmovement along the soil capillary was also proven. Field test of this method was carried out in an area of 6400 m2, in which wheat straw layer of 5 cm was distributed in the depth of 25 cm. After 50 days, 80% of the testing area showed a normal soil electronic conductivity (soil EC <5 mS x cm(-1)) in contrast to 17% before leaching process. The concentrations of Na+ and Cl- were decreased from 1642.5 mg x kg(-1) and 1 301.2 mg x kg(-1) to 499.3 mg x kg(-1) and 433.8 mg x kg(-1), respectively. The remediated land upon the implementation of wheat straw gave a 72% of the regular wheat production obtained from the normal farmland, while the control land without wheat straw gave 12%. These results demonstrated the effectiveness and the high potential of using wheat straw for the salt leaching in remediation of petroleum-salt contaminated soil.

A new bioaugmentation method utilizing wheat straw to enhance salt leaching and the subsequent petroleum biodegradation by consortia of bacteria and fungi was proposed. The present study aimed at the effects of wheat straw on the growth and the degradation behavior of E. cloacae and Cun. echinulata, the two species of the consortia. In the laboratory experiments, it was shown that the addition of 5% (mass fraction) straw led to an increase of biomass by 25- and 3-fold to the bacteria and fungi, respectively. The biodegradation ratio of total petroleum hydrocarbon (TPH) was elevated from 29.2% to 48.0% after 468 h treatment. The biodegradation ratio of alkane and aromatic hydrocarbons in petroleum were increased from 31.5% and 39.1%, to 55.7% and 55.9%, respectively. The field demonstration was carried in an area of 6400 m2, in which the bacteria and fungi were inoculated after salt leaching in the presence of wheat straw. The addition of wheat straw in the contaminated soil led to an increase by 158- and 9-fold to the bacteria and fungi, as compared to their counterpart in the controlland without wheat straw, at 25 days after the inoculation. The content of TPH was down to below 0.3% while the maximum biodegradation ratio of TPH reached 75% after 45 days treatment. These results demonstrated the effectiveness and high potential of the wheat straw enhanced bioaugmentation of petroleum-salt contaminated soil.

The possible factors of sludge reduction such as sludge decay, energy uncoupled metabolism, anaerobic oxidation with low sludge production were discussed in an OSA (oxic-settling-anaerobic) process. It has been confirmed that sludge decay included hydrolysis and acidogenesis of dead microorganism and particle organic carbon adsorbed in sludge flocs and endogenous metabolism. The concentrations of SCOD, NH4(+)-N, TP in supernatant were increased gradually during sludge anaerobic treatment in the batch experiments. Soluble protein were increased up to 33.09 mg/L, exceeding carbohydrate change after 16 h anaerobic sludge treatment in the OSA batch experiment. It proved sludge lysis and hydrolysis in the OSA process. Endogenous SOUR in the OSA batch test was achieved 8 mg/(g h), more than 1.7 multiples as that in the CAS batch test. Higher endogenous metabolism promoted sludge reduction in the OSA process. Sludge decay is the decisive cause in OSA process, accounting for 66.7% of sludge production reduction. By batch experiments, it has been validated energetic uncoupling in OSA system since microorganisms were exposed in alternative anaerobic and aerobic environment. It accounts for about 7.5% of sludge production reduction. SCOD released from anaerobic sludge tank in the OSA process is used as the substrate for cryptic growth. The substrate is used for anoxic denitrifying, anaerobic phosphorus release, sulfate reduction and methane production. These anaerobic reactors have lower sludge production than aerobic oxidation when consumed SCOD is equivalent, which may lead to approximately 23.5% reduction of sludge production in the OSA system. It has been concluded that multiple causes result in minimization of excess sludge in OSA system.

Pilot demonstration of the fungal-bacterial augmented in situ remediation of petroleum contaminated soil was carried out in Zhongyuan Oilfield, Henan, using artificially prepared soil, newly and aged contaminated soil as sample, respectively. For the first run of the experiment started from Nov. 5, 2004 and lasted for 122 days, the removal of contaminate was 61.0%, 48.3% and 38.3% for diesel, lube and crude oil, respectively. For the second run started from May 18, 2005 and lasted for 161 days, the removal of TPH was 75% for the artificially contaminated soil sample while 46.0% and 56.6% for the fresh and aged contaminated soil. The removal of high concentration salt was involved in the remediation of the freshly and aged contaminated soil. The changes of the petroleum composition was monitored during the remediation process, which confirmed the effective degradation of alkanes, aromatic hydrocarbons and non-hydrocarbon compounds by the fungi-bacteria consortia, as compared to that obtained without the inoculation of the consortia. To further demonstrate the remediation, wheat was planted in above reclaimed soil. While wheat production in the reclaimed artificially contaminated soil yielded nearly as much as that obtained in the normal farmland, the output of wheat in the reclaimed refresh and aged contaminated soil was 57.2% and 70.3% of the averaged output of the normal farmland. The above results further confirmed the workability of fungal-bacterial augmented in situ remediation of petroleum contaminated soil and its application potential as well.

Efficiency of pollution degradation, performance of activated sludge, effect of temperature fluctuation and recalcitrant organic compounds on system stability were investigated in OSA process for minimization of excess sludge. CAS process and OSA process were run with synthetic wastewater for 240 d. The results indicate that the OSA process excels the CAS process as a whole. COD removal efficiency in OSA process was slightly more than that in CAS. Removal efficiency of nitrogen and phosphorus could be enhanced to 42.58% and 53.84% respectively. Biological phosphorus accumulation in aerobic sludge from OSA and CAS were 2.69 g and 1.11 g per 100 g dry sludge, which further approved biological phosphorus removal in OSA process. Because of alternative aerobic and anaerobic environment in OSA process, sludge settleability and activity are improved. SVI in OSA process was 97 averagely. SOUR and dehydrogenase activity of sludge in OSA were higher appreciably than those in CAS. Protein concentration was higher above 1.69 mg x g(-1) and polysaccharide concentration was lower 6.7 mg x g(-1) in OSA sludge than those in CAS, which confirms the effect of anaerobic tank on sludge performance and microorganism diversity. Lower polysaccharide concentration in OSA sludge improves the settleability. Contrasting to CAS process, OSA process is more sensitive to impact of p-nitrophenol(PNP) and more inactive to temperature fluctuation. Temperature fluctuation led to an increase of the concentration of COD, NH4(+) -N, SS in effluent while sludge production Y(MLSS/COD) was reduced to 0.403 mg x mg(-1) and 0.227 mg x mg(-1) in CAS and OSA. When concentration of PNP was increased abruptly to 10 mg x L(-1), biological nutrient removal was ceased in OSA process. Once OSA system is impacted, it is difficult to restore.

Non-filamentous sludge bulking occurred during sludge acclimation in lab-scale bio-reactors and the characteristics, properties and degrading pollutants capability of non-filamentous sludge were analyzed. Both low DO concentration (0 - 0.7 mg/L) and low ratio of P/BOD5 (0.78/100) resulted in excessive proliferation of viscous zoogloea and sludge bulking. SVI was directly proportional to extracellular polysaccharides and was inversely proportional to hydrophobicity of sludge. The sludge bulking could be effectively controlled by increasing DO concentration and P/BOD5 ratio. Besides, adding some porous padding into viscous bulking sludge was a useful method which might avoid the deterioration of sludge settlement and maintain good performance in the system. The viscous bulking sludge could not be controlled by addition of NaC1O.