Enhanced nitrogen removal by an isolated aerobic denitrifying strain in a vertical-flow constructed wetland.

The addition of bacterial agents is an effective method for improving nitrogen removal from wetlands. Herein, an aerobic denitrifier, RC-15, was added to a vertical-flow constructed wetland (CW), and the presence of functional genes and microbial communities was investigated at different CW depths. For the RC-15-treated CW, the removal of NO3- and TN during the process was significantly greater than in the control. Quantitative PCR revealed that nirS is a dominant denitrifying gene for treating WWTP tailwater. Moreover, the presence of the RC-15 strain significantly enhanced the abundance of the napA gene and nirK gene in the CWs. The napA gene was concentrated in the upper layer of the CWs, and the nirK gene was concentrated in the middle and bottom layers. Compared to the control, the addition of the bacterial agent Trial resulted in a more diverse denitrification pathway, a greater abundance of 16Sr RNA, and a greater number of denitrifying strains. According to the microbial community analysis, Proteobacteria and Chloroflexi dominated denitrification in the CWs. Greater abundances of Thauera, Aeromonas and Ardenticatenales were found at the genus level, indicating that these genera have potential applications in future nitrogen removal projects.

Biofilm-developed biomass residues as novel bulking agents and microbial carriers for synergistically enhanced bioevaporation: Degradation potential and contribution to metabolic heat.

Economical and easily prepared bulking agents and microbial carriers are essential in the practical application of bioevaporation process. Biofilm-developed biomass residues not only provide structural support and microbial sources but also may contribute metabolic heat to the bioevaporation process, achieving the enhanced water evaporation and synergistic treatment of biomass residues. In this study, biofilm was cultivated on the rice straw, wheat straw, sawdust, corncob, luffa cylindrica and palm first, then those biofilm-developed biomass residues were successfully used as the bulking agents and microbial carriers in food waste bioevaporation. The degradation potential (volatile solid degradation ratio) of those biomass residues was in the order of corncob (23.96%), wheat straw (21.12%), rice straw (14.57%), luffa cylindrica (11.02%), sawdust (-2.87%) and palm (-9.24%). It's primarily the degradation of the major components, cellulose and hemicellulose, in corncob and wheat straw governed the metabolic heat contribution (91.73 and 79.61%) to the bioevaporation process. While the high lignin content in sawdust (14.57%) and palm (28.62%) caused negligible degradation of cellulose and hemicellulose, hence made them only function as structural supporter and did not contribute any metabolic heat. Moreover, though the metabolic heat contribution of rice straw and luffa cylindrica reached 58.19 and 37.84%, their lowest lignocellulose content (62.99 and 65.95%) and their lower density, as well as the dominated Xanthomonas (bacteria) and Mycothermus (fungi) led to their rapid collapse during the repeated cycles of bioevaporation. The greatest abundance of thermophilic bacteria (22.3-88.0%) and thermophilic fungi (82.0-99.3%) was observed in the corncob pile. Furthermore, considering the Staphylococcus (pathogenic bacteria) and Candida (animal pathogen) was effectively inhibited, the biofilm-developed corncob was the most favorable bulking agents and microbial carrier for the synergistic bioevaporation of highly concentrated organic wastewater and biomass residues.

Ventilation induced evolution pattern of archaea, fungi, bacteria and their potential roles during co-bioevaporation treatment of concentrated landfill leachate and food waste.

To obtain a favorable aeration type in co-bioevaporation treatment of concentrated landfill leachate and food waste, and to deeply understand the co-bioevaporation mechanisms, the temporal evolution differences of archaea, fungi and bacteria as well as the related microbial metabolism genes and functional enzymes under intermittent ventilation (IV) and continuous ventilation (CV) were investigated. Results through metagenomics analysis showed that the less sufficient oxygen and longer thermophilic phase in IV stimulated the vigorous growth of archaea, while CV was beneficial for fungal growth. Even genes of carbohydrates and lipids metabolism and ATP-associated enzymes (enzyme 2.7.13.3 and 3.6.4.12), as well as peptidoglycan biosynthesis enzyme (enzyme 3.4.16.4), were more abundant in CV, IV hold better DNA repair ability, higher microbial viability, and less dehydrogenase sensitivity to temperatures due to the critical contribution of Pseudomonas (3.1-45.9%). Furthermore, IV consumed a similar amount of heat for water evaporation with nearly half of the ventilation of CV and was a favorable aeration type in the practical application of co-bioevaporation.

Organic loading on biochemical fractions degradation pattern during food waste bioevaporation.

More food waste (FW) is desired to be treated in a certain processing period, while the degradation pattern of biochemical fractions during FW bioevaporation was significantly influenced by the organic loading (OL). Lower OL facilitated the lipids degradation, while higher OL favored the protein degradation. It was the more porous structure and abundant oxygen accelerated the lipids degradation, and the rapid proliferation of aerobic microorganisms compensated for the low protein degradation in lower OL. Detailly, 76.8% of the lipids was degraded in the trial with OL of 1.04 kg VSFW/kg TSBS (Trial A), but in the trial with OL of 3.16 kg VSFW/kg TSBS (Trial C) it was only 0.5%. For protein, the degradation was different that 17.5% of the protein was degraded in Trial A, whereas 69.1% was degraded in Trial C. Lipids degradation contributed 63.0% to the metabolic heat in Trial A, but its contribution in Trial C was only 0.5%. For protein, it contributed 4.1% to the metabolic heat in Trial A, but in Trial C it accounted for 53.6%. In addition, the degradation of carbohydrates (71.6-80.8%) and their contribution to metabolic heat (32.8-45.9%) were comparable in all trials, thus OL had little effect on carbohydrates degradation. Results from this study could provide important guideline for FW practical disposal during their biological treatment.

Temperature models for quantifying groundwater seepage flux applied in a deep lake of a plateau: Yangzonghai Lake, Yunnan, China.

Groundwater discharge from a water spring located along the southwest bank of Yangzonghai Lake, the largest deep plateau-lake with arsenic contamination in a typical karst landform, maybe a potential and on-going source of pollution, but seepage flux has not been investigated. This study applied temperature models to locate sites of groundwater discharge and quantify the magnitude and direction of seepage flux. The contaminant levels and spatial distributions, seasonal seepage flux distributions and the conductivity were investigated. The arsenic concentration of the water spring was 1481.9 µg L-1, and as the distance from the water spring increased, the arsenic concentration in the overlying water, pore-water and surface sediments decreased. Herein, the temperature models of McCallum and Bredehoeft were applied to estimate the lakebed vertical seepage flux in groundwater-surface water exchange systems during a period of 30-day in summer and winter. An upward flow of groundwater discharge was observed near the water spring, with the value of some sites over 10 cm day-1, and a downward flow was observed with increasing distance from the water spring in summer. Additionally, a slight upward flow was observed in winter. The arsenic levels, spatial distributions and the conductivity in monitoring sites were closely related to the seepage flux. The application provided a scientific basis for the prediction of groundwater-surface water exchange in deep plateau-lake and was a further development in temperature models.

Evolution of enzyme activity, heavy metals bioavailability and microbial community in different temperature stages of the co-bioevaporation process.

Laboratory investigations documented enzyme activity, heavy metals' bioavailability and the bacterial community during co-bioevaporation treatment of food waste and landfill leachate. The activities of dehydrogenase, protease, urease and phosphatase were sensitive to the changes in operating temperature inherent in co-bioevaporation. The maximum dehydrogenase activity was appeared at warming 30 °C. The maximum hydrolytic activity of the microorganisms on protein, urea and phosphorus-containing organic compounds appeared at warming 50 °C. The bacteria mainly gathered on the surface and in the pores of the sludge particles used as a bulking agent. Bacterial abundance reached its maximum at warming 50 °C. Firmicutes, Actinobacterica and Proteobacterica were the dominant bacterial phyla involved. Even though co-bioevaporation concentrated the heavy metals in the leachate, their bioavailability was substantially reduced during the process.

Spent coffee ground as a new bulking agent for accelerated biodrying of dewatered sludge.

The feasibility of using spent coffee ground (SCG) as a new bulking agent for biodrying of dewatered sludge (DS) was investigated in comparison with two other frequently-used bulking agents, air-dried sludge (AS) and sawdust (SD). Results showed that the moisture contents (MC) of 16-day DS biodrying with AS (Trial A), SCG (Trial B) and SD (Trial C) decreased from 70.14 wt%, 68.25 wt% and 71.63 wt% to 59.12 wt%, 41.35 wt% and 57.69 wt%, respectively. In case of Trial B, the MC rapidly decreased to 46.16 wt% with the highest water removal (70.87%) within 8 days because of the longest high-temperature period (5.8 days). Further studies indicated that the abundant biodegradable volatile solids (BVS) and high dissolved organic matter (DOM) contents in SCG were the main driving forces for water removal. According to pyrosequencing data, Firmicutes, most of which were recognized as thermophiles, was rapidly enriched on Day 8 and became the dominant phylum in Trial B. Four thermophilic genera, Bacillus, Ureibacillus, Geobacillus and Thermobifida, which can produce thermostable hydrolytic extracellular enzymes, were the most abundant in Trial B, indicating that these thermophilic bacteria evolved during the long high-temperature period enhanced the biodegradation of BVS in SCG. The 8-day biodried product of Trial B was demonstrated to be an excellent solid fuel with low heating value (LHV) of 9284 kJ kg-1, which was 2.1 and 1.8 times those of biodried products with AS and SD, respectively. Thus SCG was found to be an excellent bulking agent accelerating DS biodrying and producing a solid fuel with a high calorific value.

Combustion characteristics of biodried sewage sludge.

In this study, effects of biodrying on the characteristics of sewage sludge and the subsequent combustion behavior were investigated. 7-Day of biodrying removed 49.78% of water and 23.17% of VS initially contained in the sewage sludge and increased lower heating value (LHV) by 37.87%. Meanwhile, mass contents of C and N decreased from 36.25% and 6.12% to 32.06% and 4.82%, respectively. Surface of the biodried sewage sludge (BDSS) appeared granulated and multi-porous, which was thought to facilitate air transfer during combustion. According to thermogravimetric (TG) analysis coupled with mass spectrometer (MS) with a heating rate of 10 °C/min from 35 °C to 1000 °C, thermally-dried sewage sludge (TDSS) and BDSS lost 74.39% and 67.04% of the initial mass, respectively. In addition, combustibility index (S) of BDSS (8.67 × 10-8 min-2 K-3) was higher than TDSS. TG-MS analyses also showed that less nitrogenous gases were generated from BDSS than TDSS. It was again showed that the average CO and NO concentrations in exit gas from isothermal combustion of BDSS were lower than those from TDSS, especially at low temperatures (≤800 °C). Based on these results, it was concluded that biodrying of sewage sludge was an energy-efficient water-removal method with less emission of air pollutants when BDSS was combusted.

Mitigating 17α-ethynylestradiol water contamination through binding and photosensitization by dissolved humic substances.

Photodegradation is an important abiotic pathway transforming organic pollutants in natural waters. Humic substances (HS), including humic and fulvic acids, are capable of accelerating the photodegradation of steroid estrogens. However, how the photodegradtion of the emerging pollutants influenced by HS is not clear. Thus, we studied the roles and mechanisms of HS in inducing the photodegradation of 17α-ethynylestradiol (EE2). HS generally induces EE2 photodegradation through binding and reactive species generation. Apart from hydroxyl radical (HO), the excited triplets of humic substances (3HS*) are other key reactive species degrading EE2 by abstracting electrons. HO and 3HS* were responsible for about 60% of the overall EE2 photodegradation at 250µmol HS L-1. Most of EE2 molecules bound to the HS via H-bonding, π-π and hydrophobic interactions. The binding role of HS in promoting EE2 photodegradation was rationalized by 17ß-estradiol competitive binding with EE2 to the humic and fulvic acids. Furthermore, HS-promoted photodegradation can alter EE2 toxicity to wheat, rice and Ormosia plants. This study extends our knowledge on the photochemical behaviors and ecological risks of steroid estrogens in natural waters.

Photobleaching alters the photochemical and biological reactivity of humic acid towards 17α-ethynylestradiol.

Dissolved humic acid (HA) is ubiquitous in natural waters. Its presence significantly changes the photo-and bio-degradation of some organic pollutants in natural waters. The effects of photobleaching on the composition, photosensitizing property and bioavailability of HA were investigated here along with the subsequent influence on its photochemical and biological reactivity in mediating 17α-ethynylestradiol (EE2) degradation. Photobleaching transformed the refractory HA into some small molecules, including organic acids and aliphatics. Along with composition alteration, the photochemical reactivity of HA towards EE2 was slightly depressed, with 9% of the removal rate inhibited by a 70-h photobleaching. Contrarily, the reactivity of HA in mediating EE2 biodegradation by E. coli was significantly promoted by a short-term photobleaching. Compared to the biodegradation of EE2 in the pristine HA, the 10-h photobleached HA increased the biodegradation removal rate of EE2 by 25%, reaching its peak value of about 60%. However, the EE2 biodegradation was inhibited by further irradiation, and the removal rate of EE2 decreased to that in the pristine HA systems. Because no substrate competition was found between EE2 and formate or glucose, EE2 biodegradation mediated by HA in natural waters may not be affected by coexistent organics. Photodegradation and biodegradation of EE2 mediated by HA thus can be combined together by photobleaching to remove pollutants from natural waters. The results reported here could assist environmental risk assessment with respect to EE2 in natural aquatic systems.

Novel bioevaporation process for the zero-discharge treatment of highly concentrated organic wastewater.

A novel process termed as bioevaporation was established to completely evaporate wastewater by metabolic heat released from the aerobic microbial degradation of the organic matters contained in the highly concentrated organic wastewater itself. By adding the glucose solution and ground food waste (FW) into the biodried sludge bed, the activity of the microorganisms in the biodried sludge was stimulated and the water in the glucose solution and FW was evaporated. As the biodegradable volatile solids (BVS) concentration in wastewater increased, more heat was produced and the water removal ratio increased. When the volatile solids (VS) concentrations of both glucose and ground FW were 120 g L(-1), 101.7% and 104.3% of the added water was removed, respectively, by completely consuming the glucose and FW BVS. Therefore, the complete removal of water and biodegradable organic contents was achieved simultaneously in the bioevaporation process, which accomplished zero-discharge treatment of highly concentrated organic wastewater.

Life cycle analyses of CO2, energy, and cost for four different routes of microalgal bioenergy conversion.

With a target production of 1000 ton of dry algae/yr, lipid content of 30 wt.%, and productivity of 30 g/m(2)-d in a 340-day annual operation, four common scenarios of microalgae bioenergy routes were assessed in terms of cost, energy, and CO2 inputs and outputs. Scenario 1 (biodiesel production), Scenario 2 (Scenario 1 with integrated anaerobic digestion system), Scenario 3 (biogas production), and Scenario 4 (supercritical gasification) were evaluated. Scenario 4 outperformed other scenarios in terms of net energy production (1282.42 kWh/ton algae) and CO2 removal (1.32 ton CO2/ton algae) while Scenario 2 surpassed the other three scenarios in terms of net cost. Scenario 1 produced the lowest energy while Scenario 3 was the most expensive bioenergy system. This study evaluated critical parameters that could direct the proper design of the microalgae bioenergy system with an efficient energy production, CO2 removal, and economic feasibility.