Reuse of secondary municipal effluent from wastewater treatment plants in water bodies could effectively alleviate freshwater resource shortage. However, excessive nutrients must be efficiently ...removed to prevent eutrophication. Compared with other means of advanced wastewater treatment, microalgae-based processes display overwhelming advantages including efficient and simultaneous N and P removal, no requirement of additional chemicals, O
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mitigation, and potential value-added products from harvested biomass. One particular challenge of microalgae-based advanced municipal wastewater treatment compared to treatment of other types of wastewater is that concentrations of nutrients and N:P ratios in secondary municipal effluent are much lower and imbalanced. Therefore, there should be comprehensive considerations on nutrient removal from this specific type of effluent. Removal of nutrients and organic substances, and other environmental benefits of microalgae-based advanced municipal wastewater treatment systems were summarized. Among the existing studies on microalgal advanced nutrient removal, much information on major parameters is absent, rendering performances between studies not really comparable. Mechanisms of microalgae-based nitrogen and phosphorus removal were respectively analyzed to better understand advanced nutrient removal from municipal secondary effluent. Factors influencing microalgae-based nutrient removal were divided into intrinsic, environmental, and operational categories; several factors were identified in each category, and their influences on microalgal nutrient removal were discussed. A multiplicative kinetic model was integrated to estimate microalgal growth-related nutrient removal based majorly on environmental and intrinsic factors. Limitations and prospects of future full-scale microalgae-based advanced municipal wastewater treatment were also suggested. The manuscript could offer much valuable information for future studies on microalgae-based advanced wastewater treatment and water reuse.
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CEKLJ, DOBA, EMUNI, FZAB, GEOZS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
UV-C irradiation has drawn much attention in recent years as a candidate for controlling harmful algal blooms (HABs). In this review, we have collated the recent knowledge about the UV-C irradiation ...technique for suppressing HABs, including the effectiveness, mechanisms, influencing factors, growth recovery pattern, and UV-C irradiation facilities. Most microalgal species have been proved to be effectively suppressed by UV-C irradiation and the suppression effects had positive correlation with UV-C dose. However, the effectiveness on difference algal species varied dramatically. The understanding for growth suppression mechanisms upon UV-C irradiation has been significantly deepened beyond pyrimidine dimers. The suppression effects on algal cell density were the results of UV-induced damage on nucleic acid, light harvesting and electron transfer and transportation, nitrogen fixation and assimilation, toxin synthesis, settle ability, antioxidative capacity and cellular membrane integrity. While several influencing factors, such as algal sensitivities, UV transmittance (UVT), salinity, pH, and microalgal growth recovery should be paid attention to in practical application. UV-C facilities with high maturity, especially flow-through reactors, make it possible to develop ship-born UV-C facilities and put UV-C irradiation technique into real practice on controlling HABs.
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•UV-C irradiation could suppress microalgal growth in a dose-dependent mode.•Mechanisms and factors affecting microalgal growth suppression were systematically reviewed.•Microalgal growth recovery after UV-C exposure and its mechanisms were discussed.•UV-C irradiation facilities for microalgal growth suppression were reviewed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The risk of harmful algal blooms (HABs) in the water recharged with reclaimed water is a bottleneck for water reuse. The suppression effects and mechanisms of the combination of UV-C and berberine on ...Microcystis aeruginosa and Scenedesmus obliquus in reclaimed water were investigated. Mono UV-C irradiation at 75 mJ cm−2 could suppress the growth of M. aeruginosa for 7 d and that at 90 mJ cm−2 could suppress the growth of S. obliquus for 5 d. UV-C irradiation combined with 0.2–2 mg L−1 berberine lengthened the inhibition period of M. aeruginosa to 10- > 22 d and that of S. obliquus to 7- > 22 d and induced more rapid lethal effects on the harmful microalgal cells, in significant synergetic patterns. The combination of UV-C and berberine suppressed total, intracellular and extracellular microcystin-LR (MC-LR) more effectively and decreased the MC-LR quota significantly, which further reduced the risks of microcystin production and release. Furthermore, synergetic mechanisms of the combined treatments were systematically investigated from the aspects of photosynthetic system (photosynthetic activity and pigments), metabolic activity (ATP and membrane potential), oxidation stress (reactive oxygen species (ROS) and glutathione (GSH)), and apoptosis-like cell death (phosphatidylserine (PS) ectropion, caspase-3 activity and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive rate). The combination treatment provided a joint attack of UV-C and berberine on photosynthetic transport chain of photosynthetic system II (PS II), and a synergetic pathway to achieve more severe disruptions in energy metabolism as well as aggravated oxidative stress. The accumulated ROS enhanced increases in programmed cell death (PCD) indicators of both microalgal species, which contributed to the enhancement effects on growth suppression. The results showed that the combination treatment achieved lower dose requirements of both UV-C irradiation and berberine for inducing the same inhibition effects on microalgal cells, which was promising to be applied in the HABs control of reclaimed water.
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•The growth suppression effects of combined UV-C and berberine on microalgae were investigated.•Significant synergetic effects between UV-C and berberine were observed.•UV-C/berberine further reduced the risks of microcystin production and release.•Synergetic mechanisms of the combination treatments were systematically investigated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Effects of auxins on the growth and FAMEs of microalgae were investigated.•The auxins showed a “low dosage-promotion and high dosage-inhibition effect”.•The IAA increased the monounsaturated fatty ...acid (MUFA) content.•Auxin enhanced the photosynthetic activity may via increasing chlorophyll contents.
Microalgae are potential candidates for the production of valuable products, such as renewable biodiesel, health products and pigments. However, low biomass productivity has restricted their large-scale applications. In this study, the effects of two auxins (one natural type of indole-3-acetic acid (IAA) and the other synthetic type of 2,4-dichlorophenoxyacetic acid (2,4-D)) on the growth and fatty acid methyl esters (FAMEs) production of a freshwater microalgae Scenedesmus sp. LX1 were investigated. Both auxins showed a “low dosage-promotion and high dosage-inhibition” effect on the growth and FAMEs accumulation. The optimum dosage of IAA and 2,4-D were 1mgL−1 and 0.1mgL−1, respectively. Moreover, the IAA could increase the monounsaturated fatty acid content. The auxins may promote the growth by enhancing the photosynthetic activity through increasing chlorophyll contents. Therefore, auxin significantly enhanced microalgal growth and FAMEs accumulation, and has a potential for application in developing efficient microalgal cultivation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Nowadays, microalgae-based bioenergy has been commonly considered as a potential substitute of the non-renewable traditional energy resources with increasing attention. Nevertheless, microalgal cells ...will secrete/release some Soluble Algal Products (SAPs) into the culture medium during microalgal biomass cultivation. Studies on the influences, especially the negative ones, of SAPs in large-scale cultivation of microalgae for biomass/bioenergy production remain limited. The negative effects, properties, production and treatments of SAPs were therefore investigated and summarized in this paper. It was found that SAPs may inhibit microalgal growth, raise the cost of microalgal recovery and lower the performance of the downstream discharged water treatment process after microalgal cultivation, among others. The production of SAPs could be as high as 70mg/L in terms of dissolved organic carbon (DOC), causing substantial environmental issues. The chemical properties of SAPs significantly varied among different microalgal species, growth phases and nutrient concentrations. The distribution of molecular weight of SAPs varied from less than 1kDa to more than 100kDa, meanwhile the hydrophilic/hydrophobic property of SAPs showed a consistency. All studies showed that more than 60% of SAPs are hydrophilic. After comparing three different SAPs treatment methods, it was concluded that biodegradation could be a feasible and economical process to remove SAPs based on the properties of SAPs. The mechanisms of SAPs formation and the mitigation of their undesirable effects are still not clear. Therefore, a systematic and deep study on those topics is urgently needed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Cyanobacterial blooms (CBs) in eutrophic lakes can cause various harmful issues to both humans and animals, disturb drinking water supply, and devastate lake ecosystems. Although great progresses ...have been made in many lakes from China and abroad on CBs prevention, mitigation and control, systematic research on the influencing factors of CBs in hypereutrophic plateau Lake Dianchi over a long time span is so far unavailable. This study comprehensively generalized both meteorological and water quality changes in Lake Dianchi during 1990–2015 on both yearly and monthly basis, separated Caohai from Waihai of Lake Dianchi regarding water quality variations, and investigated the individual and joint influencing meteorological and water quality factors on CBs using Spearman correlation, principal component analysis, and multivariate linear stepwise regression. Four specific lake regions, i.e. Caohai, northern Waihai, central Waihai, and southern Waihai, were respectively analyzed due to significant water quality heterogeneity. Results indicated that mild temperatures, low wind velocities, and hypereutrophic water conditions all favor CBs in Lake Dianchi, and the significant temperature rising trend may exacerbate severer CBs in the future. Despite configuration differences, the first principal components on CBs in the four sub-regions of Lake Dianchi were all consisted of meteorological factors, while water quality parameters especially total phosphorus concentrations contributed to the second principal component. Quantification of joint meteorological and water quality influencing factors on CBs needs further improvement, and largely relies on the accuracy of future weather forecasts, in order to set the goal of water quality improvement in each specific lake region for effective CBs management.
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•Meteorological and water quality changes in Lake Dianchi (1990–2015) were analyzed.•The lake was divided into four sub-regions based on water quality heterogeneity.•In all regions, meteorological factors were the first principal component on CBs.•Meanwhile, water quality especially nutrients were the second principal component.•Accurate weather forecast helps to set the water quality standards across the lake.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In many microalgal cultivation systems, microalgae co-exist with bacteria, while little is known about the characteristics of their symbiotic relationships. In this study, twenty-six microalgae ...growth-promoting bacteria were isolated from a culture system of Scenedesmus sp. LX1 cultivated in the secondary effluent from domestic wastewater by using the high-throughput multiple well plate screening method. Ten strains were found to produce and secrete indole acetic acid (IAA), promoting the growth of microalgae. Meanwhile, the microalgae might have secreted signal substances to induce IAA production in bacteria, which was amplified in the tryptophan abundant environment. This indicates that bacteria may mainly promote the growth of the co-existing microalgae through secreting IAA, and microalgae would selectively enhance IAA secretion in turn. Microalgae cultured with microalgal growth-promoting bacteria would be a new potential strategy for improving large-scale microalgal cultivation in an economic and environmentally-friendly way.
•High-throughput screening method was used to isolate microalgae promoting bacteria.•Ten of twenty-six isolates secret indole acetic acid to enhance microalgal growth.•Indole acetic acid is an important signal matter between microalgae and bacteria.•The indole acetic acid secretion of symbiotic bacteria is enhanced by microalgae.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
While reverse osmosis (RO) is a promising technology for wastewater reclamation, RO concentrate (ROC) treatment and disposal are important issues to consider. Conventional chemical and physical ...treatment methods for ROC present certain limitations, such as relatively low nitrogen and phosphorus removal efficiencies as well as the requirement of an extra process for hardness removal. This study proposes a novel biological approach for simultaneous removal of nitrogen, phosphorus, and calcium (Ca2+) and magnesium (Mg2+) ions from the ROC of municipal wastewater treatment plants by microalgal cultivation and algal biomass production. Two microalgae strains, Chlorella sp. ZTY4 and Scenedesmus sp. LX1, were used for batch cultivation of 14–16 days. Both strains grew well in ROC with average biomass production of 318.7 mg/L and lipid contents up to 30.6%, and nitrogen and phosphorus could be effectively removed with efficiencies of up to 89.8% and 92.7%, respectively. Approximately 55.9%–83.7% Ca2+ could be removed from the system using the cultured strains. Mg2+ removal began when Ca2+ precipitation ceased, and the removal efficiency of the ion could reach up to 56.0%. The most decisive factor influencing Ca2+ and Mg2+ removal was chemical precipitation with increases in pH caused by algal growth. The results of this study provide a new biological approach for removing nitrogen, phosphorous, and hardness from ROC. The results suggest that microalgal cultivation presents new opportunities for applying an algal process to ROC treatment. The proposed approach serves dual purposes of nutrient and hardness reduction and production of lipid rich micro-algal biomass.
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•Chlorella sp. ZTY4 and Scenedesmus sp. LX1 could adapt well to the RO concentrate.•Average biomass production was 136.9 mg/L and lipid contents were up to 32.0%.•Up to 89.8% nitrogen and 92.7% phosphorus were removed from ROC.•Hardness ions (Ca2+ and Mg2+) could be efficiently removed from ROC.•Precipitation by algae-induced pH rise was the decisive factor for hardness removal.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
To evaluate the efficacy and safety of caudal dexmedetomidine in pediatric caudal anesthesia (CA).
We searched PubMed, Embased, and Cochrane Library (from inception to June 2019) for eligible ...studies. The primary outcomes were the time to first analgesia, time of postoperative eye opening, intraoperative endtidal sevoflurane concentration, and postoperative sedation score. We calculated pooled risk ratios (RR) and 95% CIs using random- or fixed-effects models.
Thirteen trials involving 793 patients were found. Meta-analysis showed that the time to first rescue pain medication and the time from the end of anesthesia to eye opening in the CA+dexmedetomidine group were significantly longer than in the CA group (P < .00001). The intraoperative end-tidal sevoflurane concentration in the CA+dexmedetomidine group was significantly decreased (P < .00001). Dexmedetomidine appeared to increase the rate of bradycardia in the CA+dexmedetomidine group (P = .04). Additionally, the sedation score in the CA+ dexmedetomidine group was significantly higher at 2 hours after the operation compared with the CA group (P < .00001 at 2 hours).
Caudally administered dexmedetomidine is a good alternative for prolonging postoperative analgesia with less pain, decreased intraoperative end-tidal sevoflurane concentration, and full postoperative sedation.
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