Internal loading regulates the phosphorus concentration in a diversion input shallow lake in the semi-humid region of North China: Differentiated processes in littoral wetland and open water areas.

Diversion input lakes usually have a low catchment area/lake area ratio and pulsing pollution input. Various pollutants might accumulate in the lake continuously owing to the concentration effect under high evaporation but low precipitation over the entire area, typically for sedimentary cyclic elements such as phosphorus (P). However, the detailed transportation, sedimentation, and internal release mechanisms of P in the diversion input lakes remain unclear. This study conducted a year-long investigation of the littoral wetlands and open water areas of the shallow Lake Hengshui in the semi-humid region of North China. Results revealed that the average total P concentrations in the water and surficial sediment reached as high as 0.202 mg L-1 and 878.21 mg kg-1 in summer. The high water P levels in the lake were mainly regulated by the high internal P loading during summer and autumn, with the internal P loading being approximately nine times the external P loading. The littoral wetland area serves as a higher sedimentation sink and release source of P than the open water area. The concentrated P was continuously transported to the littoral wetland area through detritus burial, coprecipitation, and deposition of suspended particles. The release of P was mainly controlled by the dissolution of redox-sensitive Fe-P and Org-P at high temperatures and organic matter mineralization in the sediment, accompanied by the potential release capacity of apatite P (Ca-P). Future management of eutrophication and P levels in similar diversion input lakes should pay more attention to the high internal P loading in the sediment and the differentiated sedimentation and release processes in the littoral wetland and open water areas.

An assessment of the purification performance and resilience of sponge-based aerobic biofilm reactors for treating polluted urban surface waters.

Pollutants are continuously released into surface waters, which decrease the dissolved oxygen (DO) concentration and leads to the formation of black-odorous water, especially in slow-flowing urban lakes and enclosed small ponds. In situ treatment by artificial aeration or water cycling, coupled with biofilm, can address this problem without occupying large amounts of land. In this study, we designed a novel sponge-based aerobic biofilm reactor (SABR) and evaluated its performance in purifying urban surface water under different conditions. In the urban lake water treatment, the continuous inflow results revealed that the NH4+-N and NO2--N concentrations in the effluent were stable and remained lower than 0.10 mg/L and 0.05 mg/L, respectively. Abrupt increases in the NH4+-N and NO2--N concentrations in the influent and sudden increases in the NH4+-N and NO2--N concentrations in the effluent were observed, and only 4 to 8 days were required for the concentrations to decline below 0.10 mg/L and 0.05 mg/L, respectively. Increases in the polyurethane sponge filling ratios in the SABRs can reduce the DO concentration but do not affect NH4+-N removal. When no biodegradable organic matter was present in the enclosed surface water, the degradation time of NH4+-N from 14.22 to 0.10 mg/L was only 9 days when SABRs were combined with water cycling, which was shorter than the time needed by water cycling alone (16 days), and most of the NH4+-N was converted to NO3--N. When massive amounts of biodegradable organic matter were present in the enclosed surface water, 22 days were required to remove the NH4+-N when SABRs were combined with water cycling. Our results indicated that organic matter could be used as a carbon source to eliminate the produced NO3--N in SABRs. Therefore, the newly developed bioreactor provides an effective approach for treating N-polluted urban surface waters.

Reliance and effect of sediment bulking on the physicochemical properties of sediments in aquatic environments.

Sediment bulking is intently related to the occurrence of black water agglomerate, sediment resuspension and erosion in aquatic environments. In this study, five different lake sediments were sampled to study effects of sediment characteristics on sediment bulking and then investigate how sediment bulking affected in turn sediment physicochemical properties. Within 30 days of experiments, the sediment properties showed an obvious influence on variation in sediment height (VSH) ranging from only 0.03 to 1.26 cm for five sediment samples. It was found that labile nutrients were closely related to the VSH (P < 0.05) during sediment bulking. In addition, the high-throughput sequencing revealed that the microbial communities in sediments associated with degradation of organic matter and anaerobic environments, were also related to sediment bulking. Through comparing sediments with and without bulking, it was found that sediment bulking would clearly increase the proportion of air around 2.14 times, and reduce the critical shear stress of sediment with a decrease by 67.33% after 30 days, which favored sediment resuspension and erosion. Thus, this study could provide a deep insight in the key factors and the environmental effects of sediment bulking, and then be helpful in protecting the aquatic environments against ecological disasters.

Enhanced nitrate removal from surface water in a denitrifying woodchip bioreactor with a heterotrophic nitrifying and aerobic denitrifying fungus.

A heterotrophic nitrifying and aerobic denitrifying fungus was isolated from lake water and identified as Penicillium tropicum strain IS0293. The strain exhibited efficient heterotrophic nitrification-aerobic denitrification ability and could utilize ammonium, nitrite and nitrate as a sole nitrogen source. Batch tests demonstrated that strain IS0293 can remove nitrate using variety of organic carbon compounds as carbon sources. The effect of woodchip leachate collected at different degradation times on denitrification performance of the strain was also investigated. Furthermore, two denitrifying woodchip bioreactors were constructed to assess the bioaugmention of strain IS0293 for nitrate removal from surface water. Results demonstrated that the incubation of strain IS0293 enhanced the nitrate removal efficiency of the bioreactor. In addition, the average effluent TOC content of the bioaugmention bioreactor was 38.22% lower than the control bioreactor. This study would be valuable to develop an effective technology for nitrate-laden surface water under aerobic conditions.

Mesocosm experiment reveals a strong positive effect of snail presence on macrophyte growth, resulting from control of epiphyton and nuisance filamentous algae: Implications for shallow lake management.

Increased nutrient loading has adverse effects on the growth of submerged macrophytes in eutrophic shallow lakes. Where growth of phytoplankton, epiphyton and filamentous algae is excessive, all may contribute to shading that limits macrophyte growth. However, when abundant, herbivorous snails may dampen this effect by reducing the biomass of epiphyton, and perhaps also of nuisance filamentous algae, both which have the potential to become more abundant in a future warmer world. We studied the effects of herbivorous snails (Radix swinhoei) on the biomass of phytoplankton, epiphyton and filamentous algae as well as the growth of the submerged macrophyte, Vallisneria denseserrulata, under contrasting nutrient loadings (low, nitrogen (N) 113 µg L-1·d-1 and phosphorus (P) 10 µg L-1·d-1; high, N 339 µg L-1·d-1 and P 30 µg L-1·d-1) in a 30 day outdoor mesocosm experiment, conducted on the shore of subtropical Lake Taihu, China. We found significant interactive effects of nutrient loading and snail presence on biomasses of epiphyton and filamentous algae and on the biomass and relative growth rate of submerged macrophytes. When snails were absent, the biomass of epiphyton and the biomass and coverage of filamentous algae all increased markedly, while the biomass, density and relative growth rate of V. denseserrulata decreased significantly with increased nutrient loading. When snails were present, biomasses of epiphyton, phytoplankton and filamentous algae were significantly reduced and growth of V. denseserrulata significantly increased under both high and low nutrient loading scenarios, and the effect was most pronounced in the nutrient-rich treatment. The present study suggests that in shallow aquatic ecosystems, herbivorous snails reduce the negative impact of nutrient loading on submerged macrophyte growth, by controlling both epiphyton and nuisance filamentous algae. How best to protect snails from fish predation in order to realize this potential under natural conditions is a matter that warrants further studies.

Effect of organic matter derived from algae and macrophyte on anaerobic ammonium oxidation coupled to ferric iron reduction in the sediment of a shallow freshwater lake.

As a recently discovered process of nitrogen cycling, anaerobic ammonium oxidation coupled to ferric iron reduction (Feammox) has attracted more attentions. This study investigated the spatial variation of Feammox in the sediment of different zones of a shallow freshwater lake and the effect of organic matter derived from algae and macrophyte on Feammox process. The potential Feammox rates showed significant differences among sediments from algae-dominated area (ADA), transitional area in the center of the lake (TDA), and macrophyte-dominated area (MDA), and in a descending order, ADA, MDA, and TDA. The potential Feammox rate ranged from 0.14 to 0.34 mg N kg-1day-1 in the freshwater lake sediment. The potential Feammox rates of the sediment with algae or macrophyte amendment were 12.29% and 15.31% higher than the control test without algae and macrophyte amendment. The addition of algae or macrophyte to the sediment from TDA could improve the amount of HCl-extractable total Fe, Fe(III) reduction rate, and the abundance of FeRB. These results demonstrated that organic matter is one of the key regulators of Feammox process.

Development of a sediment microbial fuel cell-based biosensor for simultaneous online monitoring of dissolved oxygen concentrations along various depths in lake water.

A novel multi-cathode, single-anode system integrating a sediment microbial fuel cell -based biosensor was developed for in-situ, continuous, and online monitoring of dissolved oxygen (DO) concentrations along various depths of lake water. The signal feedback mechanism was evaluated based on a relationship between voltage and DO concentration at corresponding depths. With an external resistance of 1000 Ω, a linear relationship was found (regression coefficient, R2 = 0.9576) between voltage and DO in the range of 0-9 mg L-1. The sensor performance was further optimized under various influence factors. The results of indoor experiments indicated that the optimal anode to single cathode area ratio was 11:1. The sensor signal could also be significantly influenced by organic matter content in sediment; thus, the addition of 5% organic matter could obtain a stable anode potential and a high voltage output. Furthermore, the sensor was operated in-situ for 67 days in a lake environment, which also led to a good correlation between the voltage and DO (R2 = 0.8897). Thus, this integrated system has great potential as an early-warning program to help identify environmental risks in aquatic environments.

Anaerobic ammonium oxidation coupled to ferric iron reduction in the sediment of a eutrophic lake.

Anaerobic ammonium oxidation coupled to ferric iron reduction (Feammox) has been assumed to play an important role in nitrogen removal from ecosystems. This study assessed the potential role of Feammox in nitrogen transformation in eutrophic lake sediment using an isotope tracing technique in sediment slurry incubation experiments. Feammox was discovered in eutrophic lake sediment. A significant correlation was found between Feammox rates and iron-reducing rates. Furthermore, the positive correlations between the abundance of iron-reducing bacteria (FeRB), such as Geobacteraceae spp. and Shewanella spp., and Feammox rates indicate that Feammox was mediated by FeRB. The potential rate of Feammox in the isotopic tracer incubation treatment was 0.23-0.43 mg N kg-1 day-1. The estimated nitrogen loss caused by Feammox accounts for 5.0-9.2% of the human-induced N input annually into the eutrophic lake. Feammox alone or coupled with anaerobic ammonium oxidation (anammox) and/or denitrification may have an essential role in the nitrogen cycle within eutrophic lake sediment.

A simple method to improve the adsorption properties of drinking water treatment residue by lanthanum modification.

The loading of La can substantially enhance the adsorption capability of drinking water treatment residue (DWTR) for better recycling. Normally, the modification was based on incubation of DWTR and La solution at a certain ratio, following by solid-liquid separation and drying processes. This study attempted to simplify La loading procedures by adopting high ratio of DWTR and La solution to eliminate the solid-liquid separation, aiming to promote the potential actual production. According to the results of the short- (2 d) and long-term (30 d) P adsorption tests, the N2 gas sorption and desorption analysis, the X-ray photoelectron spectroscopy analysis, and the metal fractionation, the substantial enhanced adsorption capability of the modified DWTR was maintained and the La loading mechanisms to DWTR changed little after eliminating solid-liquid separation processes during modification; typically, La loading increased the initial P adsorption rates from 1.00 (raw DWTR) to 6.08 and 6.03 mg g-1 d-1 for the modified DWTR with and without the separation processes. Furthermore, the DWTR before and after modification had little unfavorable effect on the survival of snail Bellamya aeruginosa, while eliminating the separation processes tended to reduce the bioavailability of Al, Fe, and La in the modified DWTR. These results demonstrated that solid-liquid separation was not the key step for DWTR modification and that the developed simple modification method was feasible for La loading to DWTR, promoting the beneficial recycling in environmental remediation.

Application of a microbial fuel cell-based biosensor for the energy-saving operation of macrophyte residues bioreactor with low concentration of dissolved organic carbon in effluents.

The increasing application of plant residues bioreactor for aquatic environment remediation may release numerous dissolved organic carbon (DOC) into aquatic ecosystems. In this study, a microbial fuel cell (MFC) sensor was integrated with a macrophyte residues bioreactor (MRBR) to provide an energy-saving way for reduction of DOC concentrations in the effluent. Through re-utilization of macrophyte residues as solid carbon source, DOC concentrations in the effluent of MRBR increased to the maximum on day 5 and then dropped down rapidly to a low value, while the ratio of bioavailable DOC decreased gradually. Interestingly, it was found that there existed a linear relationship between DOC concentrations in initial residue leachate and the voltage from MFC biosensor (R2 = 0.9852). Accordingly, aerobic biofilm through aeration were applied in the upper part of MRBR to enhance the degradation of DOC prior to discharge to aquatic systems, and aeration rate was adjusted based on MFC sensor signal. Further experiments demonstrated that when voltage decreased from 0.18 V to 0.09 V, a half of aeration rate (7.5 L min-1) could still lead to a high DOC degradation efficiency (above 50%) and a low DOC concentration (∼10 mg L-1) in the reactor effluent. Thus, the integrated MFC signal could be used to regulate the aeration rate in order to obtain a low DOC concentration in effluents under an energy-saving way.

The kinetics for ammonium and nitrite oxidation under the effect of hydroxylamine.

The kinetics for ammonium (NH4(+)) oxidation and nitrite (NO2(-)) oxidation under the effect of hydroxylamine (NH2OH) were studied by respirometry using the nitrifying sludge from a laboratory-scale sequencing batch reactor. Modified models were used to estimate kinetics parameters of ammonia and nitrite oxidation under the effect of hydroxylamine. An inhibition effect of hydroxylamine on the ammonia oxidation was observed under different hydroxylamine concentration levels. The self-inhibition coefficient of hydroxylamine oxidation and noncompetitive inhibition coefficient of hydroxylamine for nitrite oxidation was estimated by simulating exogenous oxygen-uptake rate profiles, respectively. The inhibitive effect of NH2OH on nitrite-oxidizing bacteria was stronger than on ammonia-oxidizing bacteria. This work could provide fundamental data for the kinetic investigation of the nitrification process.

Stoichiometry and kinetics of the anaerobic ammonium oxidation (Anammox) with trace hydrazine addition.

Purpose of this study is to investigate the stoichiometry and kinetics of anaerobic ammonium oxidation (Anammox) with trace hydrazine addition. The stoichiometry was established based on the electron balance of Anammox process with trace N2H4 addition. The stoichiometric coefficients were determined by the proton consumption and the changes in substrates and products. It was found that trace N2H4 addition can increase the yield of Anammox bacteria (AnAOB) and reduce NO3(-) yield, which enhances the Anammox. Subsequently, kinetic model of Anammox with trace N2H4 addition was developed, and the parameters of the anaerobic degradation model of N2H4 were obtained for the first time. The maximum specific substrate utilization rate, half-saturation constant and inhibition constant of N2H4 were 25.09mgN/g VSS/d, 10.42mgN/L and 1393.88mgN/L, respectively. These kinetic parameters might provide important information for the engineering applications of Anammox with trace N2H4 addition.

The enhancement of completely autotrophic nitrogen removal over nitrite (CANON) by N2H4 addition.

The long-term addition of N2H4 to completely autotrophic nitrogen removal over nitrite (CANON) sequencing batch reactors (SBRs) recovered and enhanced their autotrophic nitrogen removal capacity while simultaneously reducing their production of NO3(-). The total nitrogen (TN) removal rate and TN removal efficiency of the process increased from 0.202±0.011 to 0.370±0.016 kg N/m(3)/d and from 65.1±3.75% to 77.4±3.8%, respectively, and the molar ratio of NO3(-) production to NH4(+) removal (MRNN) decreased to 0.058. The most effective concentration of N2H4 addition was approximately 3.99 mg/L. N2H4 could increase the specific growth rate of anaerobic ammonium-oxidizing bacteria (AnAOB) and inhibit aerobic ammonia oxidation. The electrons released from the oxidation of additional N2H4 using hydrazine dehydrogenase (HDH), which substituted the electrons from NO2(-) oxidation to NO3(-), replenished the consumption of AnAOB anabolism and significantly reduced the consequent NO3(-) production.