Performance of fish sludge solubilization and phototrophic bioconversion by purple phototrophic bacteria for nutrient recovery in aquaponic system.

Nutrient recovery from fish sludge in aquaponics is crucial to improve the economic output of a system sustainably and hygienically. Currently, fish sludge is treated using conventional anaerobic and aerobic mineralization, which does not allow the recovery of valuable nutrients in fish wastes. In this study, a two-stage approach (named as solubilization process and phototrophic bioconversion) is proposed to convert fish sludge into mineral nutrients and biomass nutrients using purple phototrophic bacteria (PPB), thereby promoting the growth of plants and fish simultaneously in aquaponics. Anaerobic and aerobic solubilization methods are tested to pretreat the fish sludge, generating substrates for PPB. Anaerobic solubilization yields 2.1 times more soluble chemical oxygen demand (SCOD) and 3.7 times more total volatile fatty acid (t-VFA) from fish sludge compared with aerobic solubilization. The anaerobic solubilization effluent indicates a CODt-VFA/SCOD of 60% and a VFA comprising 13.3% acetate and 49.0% propionate for PPB. The phototrophic bioconversion using anaerobic solubilization effluent under the light-anaerobic condition results in the highest biomass yield (0.94 g CODbiomass/g CODremoved) and the highest PPB dominance (Ectothiorhodospira, 58.7%). The anaerobic solubilization and light-anaerobic phototrophic bioconversion achieves 54.1% of carbon recovery efficiency (CRE) (in terms of COD), as well as 44.8% and 91.3% of nutrient recovery efficiency (NRE) for N and P. A novel multiloop aquaponic system combined with PPB-based nutrient recovery is proposed for the reuse of mineral nutrients and PPB biomass generated from fish sludge.

Enhanced precipitation performance for treating high-phosphorus wastewater using novel magnetic seeds from coal fly ash.

Magnetic coagulation is a promising approach for treating high phosphorous (high-P) wastewater by enhancing precipitation efficiency using magnetic particles. In this study, a cost-effective and environmentally friendly magnetic seed from coal fly ash (MS-CFA) was used as an alternative material for Fe3O4 magnetic seed (MS) coagulation. The potential effect of MS-CFA was explored to reduce the settling time and the dosage of coagulant aid of polyacrylamide (PAM) in treating high-phosphorous (high-P) simulated wastewater at 100 and 200 mg P/L. The physicochemical characteristics of MS-CFA were analysed through particle size distribution (20-100 µm), pore size distribution (14-30 nm), specific surface area (1.654 m2/g), X-ray diffraction (XRD), specific gravity (4.2), and magnetic induction intensity (49.8 emu/g). The characteristics met the requirements as magnetic coagulation material. MS-CFA was combined with polyaluminum chloride (PAC) and polyacrylamide (PAM) to improve phosphorous precipitation performance. The synergised magnetic coagulation effect using MS-CFA and PAM reduced the settling time of flocs to less than 1 min due to the high specific gravity. This represents a reduction of 90% of the settling time compared to the control using PAM alone (15 min) without MS-CFA. MS-CFA efficiently reduced PAM dosage by 83% and 87% for treating 100 and 200 mg P/L, respectively. The presence of PAM (1 mg/L for 100 mg P/L and 2 mg/L for 200 mg P/L) was imperative for binding the MS-CFA and flocs, hence increasing the particle size of the magnetic flocs. The characteristics of the magnetic flocs were analysed through microscopy, particle size distribution, zeta potential measurements, and magnetic induction intensity. The characteristics of the magnetic flocs confirmed that MS-CFA could be an alternative material for Fe3O4 as the magnetic seeds in the magnetic coagulation process for treating high-P wastewater.

Effect of aquaculture salinity on nitrification and microbial community in moving bed bioreactors with immobilized microbial granules.

The novel immobilized microbial granules (IMG) shows a significant effect of nitrification for freshwater aquaculture. However, there is lack of evaluation study on the performance of nitrification at high salinity due to the concentration of recycled water or seawater utilization. A laboratory scale moving bed bioreactor (MBBR) with IMG was tested on recycled synthetic aquaculture wastewater for the nitrification at 2.5 mg/L NH3-N daily. The results indicated that IMG showed a high salinity tolerance and effectively converted ammonia to nitrate up to 92% at high salinity of 35.0 g/L NaCl. As salinity increased from near zero to 35.0 g/L, the microbial activity of nitrite oxidation bacteria (NOB) in the IMG decreased by 86.32%. The microbial community analysis indicated that salinity significantly influenced the community structure. It was found that Nitrosomonas sp. and Nitrospira sp. were the dominant genera for ammonia oxidation bacteria (AOB) and NOB respectively at different salinity levels.

Divergence of Granular Sludges and Microbial Communities in Two Types of Anaerobic Reactors Treating Different Wastewaters.

An advanced anaerobic expanded granular sludge bed (AnaEG) and an internal circulation (IC) reactor, which were adopted to treat starch processing wastewater (SPW) and ethanol processing wastewater (EPW), were comprehensively analyzed to determine the key factors that affected the granules and microbial communities in the bioreactors. The granule size of 900 µm in the AnaEG reactor was smaller than that in the IC reactor, and the internal and external morphological structures of the granular sludge were also significantly different between the two types of reactors. The biodiversity, which was higher in the AnaEG reactor, was mainly affected by reactor type. However, the specific microbial community structure was determined by the type of wastewater. Furthermore, the dominant methanogens of EPW were mainly Methanosaeta and Methanobacterium, but only Methanosaeta was a major constituent in SPW. Compared with the IC reactor, characteristics common to the AnaEG reactor were smaller granules, higher biodiversity and larger proportion of unknown species. The comparison of characteristics between these two reactors not only aids in understanding the novel AnaEG reactor type, but also elucidates the effects of reactor type and wastewater type on the microbial community and sludge structure. This information would be helpful in the application of the novel AnaEG reactor.

Response of treatment performance and microbial community structure to the temporary suspension of an industrial anaerobic bioreactor.

In this study, a novel type of mesophilic anaerobic bioreactor-an expanded granular sludge bed (EGSB)-was utilized to explore the effect of suspending reactor operation on the treatment performance and the microbial community structure. The parameters of performance and bacterial community before and after a four-week suspension were compared for the starch processing wastewater treatment bioreactor. The results indicate that the removal rate of the organic matter remained higher than 90%, although the biomass significantly decreased after restarting the reactor. However, the relatively stable microbial community structure before the suspension was altered significantly during the restart and post-running stages. This change was primarily due to variability in satellite species and the substitution effect of different dominant bacteria. For example, some non-major carbohydrate-degrading bacteria that were sensitive to nutrition deficiency, such as Desulfovibrio and Geobacter, were dramatically reduced after the suspension. In contrast, the stress of starvation stimulated the reproduction of hydrolytic bacteria, such as Macellibacteroides. However, the high bacterial diversity index (6.12-6.65) and the longstanding core species, including Chloroflexi, Cloacimonetes, Ignavibacteriae, Thermotogae and Euryarchaeota, maintained the functional stability of the reactor. Consequently, although the total bacteria decreased significantly after reactor operation was suspended, sufficient functional bacteria supported by the high diversity, as well as the longstanding core species, guaranteed the effective degradation after suspension.

Optimization of fed-batch enzymatic hydrolysis from alkali-pretreated sugarcane bagasse for high-concentration sugar production.

Fed-batch enzymatic hydrolysis process from alkali-pretreated sugarcane bagasse was investigated to increase solids loading, produce high-concentration fermentable sugar and finally to reduce the cost of the production process. The optimal initial solids loading, feeding time and quantities were examined. The hydrolysis system was initiated with 12% (w/v) solids loading in flasks, where 7% fresh solids were fed consecutively at 6h, 12h, 24h to get a final solids loading of 33%. All the requested cellulase loading (10 FPU/g substrate) was added completely at the beginning of hydrolysis reaction. After 120 h of hydrolysis, the maximal concentrations of cellobiose, glucose and xylose obtained were 9.376 g/L, 129.50 g/L, 56.03 g/L, respectively. The final total glucan conversion rate attained to 60% from this fed-batch process.

Effects of different pretreatment methods on chemical composition of sugarcane bagasse and enzymatic hydrolysis.

Different pretreatment processes, including liquid hot water (LHW) pretreatment, sodium hydroxide (NaOH) pretreatment, and their combinative pretreatments, were conducted to improve the enzymatic digestibility and sugar recovery from sugarcane bagasse (SCB). LHW pretreatment solubilized over 82% of xylan and 42% of lignin, after which the SCB presented the poorest enzymatic digestibility. NaOH pretreatment could remove 78% of lignin and retain most of glucan. For combinative pretreatments, the sequence of two procedures had a significant effect on the chemical composition, substrate characteristic and the subsequent enzymatic hydrolysis process. LHW-NaOH pretreatment could solubilize over 92% of xylan and remove 76% of lignin, and the highest total sugar recovery of 73% was achieved after 72 h enzymatic hydrolysis. While NaOH-LHW pretreatment, which could remove nearly 84% of lignin, but only solubilize 71% of xylan, showed the highest enzymatic digestibility. The pretreatment efficiency was: NaOH-LHW>NaOH>LHW-NaOH>LHW.