Haifeng Lu

Conversion efficiency and oil quality of low-lipid high-protein and high-lipid low-protein microalgae via hydrothermal liquefaction.

Hydrothermal liquefaction (HTL) is a promising technology for converting algae into biocrude oil. Here, HTL of a low-lipid high-protein microalgae (Nannochloropsis sp.) and a high-lipid low-protein microalgae (Chlorella sp.) was studied. An orthogonal design was applied to investigate the effects of reaction temperature (220-300°C), retention time (30-90 min), and total solid content (TS, 15-25%wt) of the feedstock. The highest biocrude yield for Nannochloropsis sp. was 55% at 260°C, 60 min and 25%wt, and for Chlorella sp. was 82.9% at 220°C, 90 min and 25%wt. The maximum higher heating values (HHV) of biocrude oil from both algae were ∼ 37 MJ/kg. GC-MS revealed a various distribution of chemical compounds in biocrude. In particular, the highest hydrocarbons content was 29.8% and 17.9% for Nannochloropsis and Chlorella sp., respectively. This study suggests that algae composition greatly influences oil yield and quality, but may not be in similar effects.

Hydrothermal liquefaction of harvested high-ash low-lipid algal biomass from Dianchi Lake: effects of operational parameters and relations of products.

Hydrothermal liquefaction (HTL) allows a direct conversion of algal biomass into biocrude oil, not only solving the environmental issues caused by the over-growing algae but also producing renewable energy. This study reports HTL of algae after separation from eutrophicated Dianchi Lake in China. Conversion efficiency was studied under different operational conditions via an orthogonal design, including holding temperature (HT) (260-340 °C), retention time (RT) (30-90 min) and total solid (TS) (10-20%). A highest biocrude oil yield (18.4%, dry ash-free basis, daf) was achieved at 300 °C, 60 min, and 20% (TS), due to the low contents of lipids (1.9%, daf) and proteins (24.8%, daf), and high contents of ash (41.6%, dry basis) and carbohydrates (71.8%, daf). Operational parameters significantly affected the biocrude yields, and chemical distribution of HTL products. The biocrude production also related to other HTL products, and involved chemical reactions, such as deoxygenation and/or denitrogenation.

Recovery of reducing sugars and volatile fatty acids from cornstalk at different hydrothermal treatment severity

This study focused on the degradation of cornstalk and recovery of reducing sugars and volatile fatty acids (VFAs) at different hydrothermal treatment severity (HTS) (4.17-8.28, 190-320°C). The highest recovery of reducing sugars and VFAs reached 92.39% of aqueous products, equal to 34.79% based on dry biomass (HTS, 6.31). GC-MS and HPLC identified that the aqueous contained furfural (0.35-2.88 g/L) and 5-hydroxymethyl furfural (0-0.85 g/L) besides reducing sugars and VFAs. Hemicellulose and cellulose were completely degraded at a HTS of 5.70 and 7.60, respectively. SEM analysis showed that cornstalk was gradually changed from rigid and highly ordered fibrils to molten and grainy structure as HTS increased. FT-IR and TGA revealed the significant changes of organic groups for cornstalk before and after hydrothermal treatment at different HTS. Hydrothermal treatment might be promising for providing feedstocks suitable for biohythane production.

Co-digestion of chicken manure and microalgae Chlorella 1067 grown in the recycled digestate: Nutrients reuse and biogas enhancement

The present investigation targeted on a sustainable co-digestion system: microalgae Chlorella 1067 (Ch. 1067) was cultivated in chicken manure (CM) based digestate and then algae biomass was used as co-substrate for anaerobic digestion with CM. About 91% of the total nitrogen and 86% of the soluble organics in the digestate were recycled after the microalgae cultivation. The methane potential of co-digestion was evaluated by varying CM to Ch. 1067 ratios (0:10, 2:8, 4:6, 6:4, 8:2, 10:0 based on the volatile solids (VS)). All the co-digestion trials showed higher methane production than the calculated values, indicating synergy between the two substrates. Modified Gompertz model showed that co-digestion had more effective methane production rate and shorter lag phase. Co-digestion (8:2) achieved the highest methane production of 238.71mL⋅(g VS)-1 and the most significant synergistic effect. The co-digestion (e.g. 8:2) presented higher and balanced content of dominant acidogenic bacteria (Firmicutes, Bacteroidetes, Proteobacterias and Spirochaetae). In addition, the archaea community Methanosaeta presented higher content than Methanosarcina, which accounted for the higher methane production. These findings indicated that the system could provide a practicable strategy for effectively recycling digestate and enhancing biogas production simultaneously.

Natural light-micro aerobic condition for PSB wastewater treatment: a flexible, simple, and effective resource recovery wastewater treatment process

ABSTRACT Photosynthetic bacteria (PSB) have two sets of metabolic pathways. They can degrade pollutants through light metabolic under light-anaerobic or oxygen metabolic pathways under dark-aerobic conditions. Both metabolisms function under natural light-microaerobic condition, which demands less energy input. This work investigated the characteristics of PSB wastewater treatment process under that condition. Results showed that PSB had very strong adaptability to chemical oxygen demand (COD) concentration; with F/M of 5.2–248.5 mg-COD/mg-biomass, the biomass increased three times and COD removal reached above 91.5%. PSB had both advantages of oxygen metabolism in COD removal and light metabolism in resource recovery under natural light-microaerobic condition. For pollutants’ degradation, COD, total organic carbon, nitrogen, and phosphorus removal reached 96.2%, 91.0%, 70.5%, and 92.7%, respectively. For resource recovery, 74.2% of C in wastewater was transformed into biomass. Especially, coexistence of light and oxygen promote N recovery ratio to 70.9%, higher than with the other two conditions. Further, 93.7% of N-removed was synthesized into biomass. Finally, CO2 emission reduced by 62.6% compared with the traditional process. PSB wastewater treatment under this condition is energy-saving, highly effective, and environment friendly, and can achieve pollution control and resource recovery.

Using co-metabolism to accelerate synthetic starch wastewater degradation and nutrient recovery in photosynthetic bacterial wastewater treatment technology

ABSTRACT Starch wastewater is a type of nutrient-rich wastewater that contains numerous macromolecular polysaccharides. Using photosynthetic bacteria (PSB) to treat starch wastewater can reduce pollutants and enhance useful biomass production. However, PSB cannot directly degrade macromolecular polysaccharides, which weakens the starch degradation effect. Therefore, co-metabolism with primary substances was employed in PSB wastewater treatment to promote starch degradation. The results indicated that co-metabolism is a highly effective method in synthetic starch degradation by PSB. When malic acid was used as the optimal primary substrate, the chemical oxygen demand, total sugar, macromolecules removal and biomass yield were considerably higher than when primary substances were not used, respectively. Malic acid was the primary substrate that played a highly important role in starch degradation. It promoted the alpha-amylase activity to 46.8 U and the PSB activity, which induced the degradation of macromolecules. The products in the wastewater were ethanol, acetic acid and propionic acid. Ethanol was the primary product throughout the degradation process. The introduction of co-metabolism with malic acid to treat wastewater can accelerate macromolecules degradation and bioresource production and weaken the acidification effect. This method provides another pathway for bioresource recovery from wastewater. This approach is a sustainable and environmentally friendly wastewater treatment technology.

Enhancing the auto-flocculation of photosynthetic bacteria to realize biomass recovery in brewery wastewater treatment

ABSTRACT Photosynthetic bacteria (PSB) wastewater treatment technology can simultaneously realize wastewater purification and biomass production. The produced biomass contains high value-added products, which can be used in medical and agricultural industry. However, because of the small size and high electronegativity, PSB are hard to be collected from wastewater, which hampers the commercialization of PSB-based industrial processes. Auto-flocculation is a low cost, energy saving, non-toxic biomass collection method for microbiology. In this work, the influence factors with their optimal levels and mechanism for enhancing the auto-flocculation of PSB were investigated in pure cultivation medium. Then PSB auto-flocculation performance in real brewery wastewater was probed. Results showed that Na+ concentration, pH and light intensity were three crucial factors except the initial inoculum sizes and temperature. In the pure medium cultivation system, the optimal condition for PSB auto-flocculation was as follows: pH was 9.5, inoculum size was 420 mg l−1, Na+ concentration was 0.067 mol l−1, light intensity was 5000 lux, temperature was 30°C. Under the optimal condition, the auto-flocculation ratio and biomass recovery reached 85.0% and 1488 mg l−1, which improved by 1.67-fold and 2.14-fold compared with the PSB enrichment cultivation conditions, respectively. Mechanism analysis showed that the protein/polysaccharides ratio and absolute Zeta potential value had a liner relationship. For the brewery wastewater treatment, under the above optimal condition, the chemical oxygen demand removal reached 94.3% with the auto-flocculation ratio and biomass recovery of 89.6% and 1510 mg l−1, which increased 2.75-fold and 2.77-fold, respectively.

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.

Biogas liquid digestate grown Chlorella sp. for biocrude oil production via hydrothermal liquefaction

Microalgae can not only purify and recover the nutrients from wastewater, but also be harvested as wet biomass for the production of biocrude oil via hydrothermal liquefaction (HTL). Chlorella sp. cultivated in the ultrafiltration (UF) membrane treated anaerobic digestion (AD) liquid digestate of chicken manure was used as the feedstock in this study. The present study characterized the products and investigated the elemental migration during HTL of Chlorella sp. fed with AD effluent wastewater (WW) and BG11 standard medium (ST) in 100mL and 500mL reactors under different operational conditions. Results showed that the highest oil yield of WW (38.1%, daf) was achieved at 320°C, 60min and 15% TS in 500mL reactor, which was 14.1% higher than that of ST (33.4%, daf) at 320°C, 30min and 20% TS in the same reactor. WW had a similar carbon and hydrogen distribution in the four product fractions under HTL conditions compared with ST. 43.4% and 32.4% of carbon in WW11 and ST11 were released into the biocrude and aqueous phase in 500mL reactor, respectively. As much as 64.5% of the hydrogen was transferred to the aqueous phase. GC-MS results showed that the chemical compounds in the biocrude oil from WW consist of a variety of chemical constituents, such as hydrocarbons, acids, alcohols, ketones, phenols and aldehydes. These two biocrude oils contained 17.5% wt. and 8.64% wt. hydrocarbons, and 63.7% wt. and 79.8% wt. oxygen-containing compounds, respectively. TGA results showed that 69.3%-66.7% of the biocrude oil was gasified in 30°C-400°C. This study demonstrates the great potential for biocrude oil production from microalgae grown in biogas effluent via HTL.

Microalgae cultivation and culture medium recycling by a two-stage cultivation system

Nutrients and water play an important role in microalgae cultivation. Using wastewater as a culture medium is a promising alternative to recycle nutrients and water, and for further developing microalgae-based products. In the present study, two species of microalgae, Chlorella sp. (high ammonia nitrogen tolerance) and Spirulina platensis (S. platensis, high growth rate), were cultured by using poultry wastewater through a two-stage cultivation system for algal biomass production. Ultrafiltration (UF) or centrifuge was used to harvest Chlorella sp. from the first cultivation stage and to recycle culture medium for S. platensis growth in the second cultivation stage. Results showed the two-stage cultivation system produced high microalgae biomass including 0.39 g·L–1Chlorella sp. and 3.45 g·L–1S. platensis in the first-stage and second-stage, respectively. In addition, the removal efficiencies of NH4+ reached 19% and almost 100% in the first and the second stage, respectively. Total phosphorus (TP) removal reached 17% and 83%, and total organic carbon (TOC) removal reached 55% and 72% in the first and the second stage, respectively. UF and centrifuge can recycle 96.8% and 100% water, respectively. This study provides a new method for the combined of pure microalgae cultivation and wastewater treatment with culture medium recycling.