Constructed Rapid Infiltration Systems Research Articles

Performance and microbial community in a constructed rapid infiltration system with hydrochar and coke as filler for advanced treatment of N, N-dimethylformamide

In this study, the treatment of wastewater with N, N-dimethylformamide (DMF) was carried out by a constructed rapid infiltration system (CRIS). The decontamination efficiency of the system with different fillers was investigated and the microbial communities and metabolic pathway were also analyzed. It was indicated that the removal of COD and DMF in the hydrochar-coke group (RA) and coke group (RB) were 58.91–59.93 % and 71.89–51.46 %, respectively. Compared with the influent, the average NH3-N concentration in the effluent increased by 77.04 % and 55.09 %, and the average removal rate of NO3--N by the two group was 72.95 % and 62.04 %, respectively. The abundance of DMF-degrading Paracoccus (5.10 %, 21.01 %) in the hydrochar and coke layers in RA was higher than the coke layer of RB (0.44 %), indicating that hydrochar promoted the growth and propagation of DMF-degrading bacteria. Hydrochar promoted the expression of gene PFK (0.2113 %), GADPH (0.3038 %), IDH (0.1832 %) and MDH (0.1758 %). In nitrogen metabolism, the relative abundance of glutamine synthetase was the highest. This research provided a theoretical foundation and technical support for the treatment DMF wastewater by CRIS.

Comparison of hexavalent chromium and cadmium removal from wastewater in constructed rapid infiltration system with layered double hydroxides (LDHs) modified maifanite substrates: Physical, chemical and microbial mechanism

In order to protect the ecological environment on which human beings depend, it is of great practical significance to prevent and control the heavy metal pollution in surface water. Cr(VI) in anionic form and Cd(II) in cationic form were selected to conduct the heavy metal purification experiments. Cr(VI) and Cd(II) removal by constructed rapid infiltration systems (CRIS) contain Zn-CO3-LDHs (ZnAl-CO3-LDHs and ZnFe-CO3-LDHs) coated maifanite substrates were compared. After ZnAl-CO3-LDHs coated, the Cr(VI) and Cd(II) removal amount increased by 87.53 % and 19.00 %, respectively. It could be inferred from XRD, FTIR, and Zeta potential results that the Cr(VI) physicochemical removal mechanism of maifanite changed to anion exchange, chemical bonding and electrostatic adsorption from electrostatic adsorption and chemical bonding after Zn-CO3-LDHs coated. By contrast, isomorphous replacement, electrostatic adsorption and chemical bonding of Cd(II) induced by Zn-CO3-LDHs replaced the electrostatic adsorption by natural maifanite. Additionally, the effective Cr(VI)/Cd(II) accumulation on Zn-CO3-LDHs modified maifanite reduced the microbial quantity, but increased EPS secretion and changed the community structure, which achieved the microbial Cr(VI)/Cd(II) removal through extracellular complexation and intracellular accumulation. This research result may provide essential reference for exploring the feasibility of heavy metal removal of CRIS with LDHs modified substrate.

Influence of constructed rapid infiltration system on groundwater recharge and quality

Infiltration of stormwater through green surfaces is an important means of groundwater recharge. However, the increase in constructed impervious area caused by intensive urbanization has led to a reduction in rainwater infiltration over the past decade. The constructed rapid infiltration system (CRIS) with an ample open space plays an important role in groundwater recharge. This study aims to explore the influence of stormwater (roof runoff) concentration infiltration on the groundwater table and quality in the CRIS. Groundwater table monitoring is conducted for more than 2 years (October 2017–December 2019) by continuous online monitoring combined with manual sampling. Results show that the addition of zeolite to the CRIS has a good removal effect on rainfall runoff pollutants, and the influence of stormwater concentration infiltration on groundwater quality is small when the CRIS enters the stable running stage. The increased proportion of chemical oxygen demand, N, and P in J1 are all less than 10% from 2018 to 2019, and they are less than 20% for heavy metals. The stormwater concentration infiltration can recharge groundwater and increase the groundwater depth, and the groundwater depth varies from 0.5 m to 1.5 m during the monitoring period. The influence scope of the concentrated infiltration on the groundwater table and quality is between 25 and 45 m. The response of the groundwater table and quality to the stormwater concentration infiltration of J1, 25 m away from the CRIS, exhibits hysteresis, and the lag time is about 3–4 months. Conclusion from relevant research can provide important theoretical support for the further study of groundwater recharge by the CRIS.

Effects of the aeration mode on nitrogen removal in a compact constructed rapid infiltration system for advanced wastewater treatment.

The configuration and the effective operation of constructed rapid infiltration (CRI) systems are of significance for advanced wastewater treatment. In this study, a novel CRI system was developed with a compact structure consisting of two stages, i.e., oxic and anoxic stages. The CRI system was continuously operated for about 140days under different aeration modes, i.e., tidal flow, continuous aeration, and intermittent aeration. Nitrogen removal was not desirable with tidal flow due to the insufficient oxygen supply in the oxic stage for nitrification, while continuous aeration could achieve good performance for chemical oxygen demand (COD), ammonium, total nitrogen (TN), and total phosphorus (TP) removal. By comparison, the CRI system operated with intermittent aeration was more favorable due to the effective removal ability for pollutants and relatively lower energy demand. The microbial community analysis revealed that Proteobacteria was the dominant phylum in both oxic and anoxic stages of the developed CRI system. Functional microbial groups (Plasticicumulans, Pseudomonas, and Nitrospira in the oxic stage; Thauera, Candidatus_Competibacter, and Dechloromonas in the anoxic stage) were identified for the mediation of carbon, nitrogen, and phosphorus in the system. This study evaluated the feasibility and the optimal aeration mode of the developed CRI system for advanced wastewater treatment, which could satisfy the requirement for the high standard of effluent quality.

Study on the effect of corn cob biochar on the performance of constructed rapid infiltration systems

The corn cob biochar (CCB600) was prepared at 600℃ with wasted corn cob as raw material. The modified corn cob biochar (CCB600-M) was prepared by modifying CCB600 with hydrochloric acid and ultrasonic. CCB600 and CCB600-M were added into constructed rapid infiltration (CRI) systems respectively as one of the filter materials, and their effect on wastewater treatment performance was investigated. The results showed that the average removal rates of COD, NH4+-N and TP in CRI reactor with adding CCB600-M were respectively 4.8%, 6.1% and 18.2% higher than those with adding CCB600, and respectively 9.3%, 11.4% and 39.7% higher than those without adding any biochars. The modified corn cob biochar was a new type of filter materials with excellent performance and low price, which can effectively improve the wastewater treatment performance of CRI systems.

Rare earth mine wastewater treatment via modified constructed rapid infiltration system: Nitrogen removal performance and microbial community

The treatment of ion-type rare earth mine (REM) wastewater by a modified constructed rapid infiltration system (CRIS) was explored. Meanwhile, the activities of hydroxylamine oxidase, nitrite reductase and urease in the column were measured, and the microorganisms in the system were analyzed. When the hydraulic load was 0.1 m3 m−2·d-1, the column height had a significant influence on the NH4+-N and TN removal rates. Specifically, the average NH4+-N and TN removal rates were 29.06 % and 14.83 %, respectively, for the CRIS with a 100 cm single-layer inorganic filler layer. While the average NH4+-N and TN removal rates increased to 69.70 % and 38.90 %, respectively, for the CRIS with a 140 cm double-layer inorganic filler layer. After increasing the hydraulic load from 0.1 m3 m−2·d-1 to 0.2 m3 m−2·d-1, the average NH4+-N and TN removal rates increased by 29.61 % and 15.84 %, respectively, in the long CRIS. The activities of hydroxylamine oxidase, nitrite reductase and urease in the column also improved. Nitrite reductase increased to 0.605 nitrite/min mg protein and hydroxylamine oxidase increased to 0.470 U/ mL g in the lower layer of the long CRIS. High-throughput sequencing analysis showed that the dominant bacterial phyla was mainly Proteobacteria and Planctomycetes. Pseudomonas, Bacillus and other aerobic denitrifying bacteria were detected at the genus level, as were the anaerobic denitrifying bacteria Comamonas and Thauera. These results illustrated that aerobic denitrification, anaerobic denitrification and anaerobic ammoxidation simultaneously existed during the CRIS treatment of REM wastewater to achieve TN removal. Furthermore, when using two full-scale CRIS in a series to treat actual REM wastewater, the NH4+-N removal rate reached 99.14 %.

Effect of organic matter on the anammox performance of constructed rapid infiltration systems

ABSTRACT Anaerobic ammonia oxidation (anammox) process was achieved in a constructed rapid infiltration (CRI) system and the effect of organic matter on the anammox performance and microbial community structure was investigated. The results showed that the removal efficiencies of -N, N and TN were 99.7 ± 0.3%, 99.8 ± 0.2% and 91.3 ± 0.2% respectively after 83 days of acclimation without the presence of organic matter in the influent. The average TN removal efficiency increased by 3.2%–7.7% due to the synergistic effect of anammox and denitrification at a low level of organic matter concentration (10–30 mg COD/L). At medium or high organic matter concentration (50–100 mg COD/L), denitrification gradually replaced anammox as the predominant nitrogen removal route due to its stronger ability to compete with substrate, resulting in a significant decline in anammox activity. The contribution rate of anammox to nitrogen removal dropped by 70.3% with the influent COD increased from 0 to 100 mg/L, and the TN removal efficiency decreased to 68.4 ± 3.6% since the anammox was seriously suppressed. 16S rRNA high-throughput sequencing analysis illustrated that the genus Candidatus Kuenenia was the predominant anammox bacteria (AAOB) with a relative abundance of 12.63% when no organic matter was applied. While the heterotrophic denitrifying bacteria (DNB) Thauera gradually dominated the community with the elevated organic matter introduction. The findings of this study provide useful information for the stable operation and optimal regulation of anammox in the CRI system when the influent contains organic matter.

Enhanced adsorption of hexavalent chromium and the microbial effect on quartz sand modified with Al-layered double hydroxides

To enhance the hexavalent chromium (Cr(VI)) removal performance of simulated constructed rapid infiltration systems (CRIS) with quartz sand (QS) substrate, QS coated with Al-layered double hydroxides (Al-LDHs@QS) was prepared by the co-precipitation method under alkaline conditions. A scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) were used to characterize QS before and after modification. The result showed that the Al-LDHs were successfully coated on the surface of the QS. The isotherm adsorption experiment indicated that compared with the original QS, the adsorption property of the modified QS changed from monolayered chemical adsorption to multilayered physical adsorption, perhaps because of different types of adsorption forces. Moreover, the adsorption capacity of modified QS was significantly enhanced and ZnAl-LDHs@QS had a maximum adsorption capacity (1428.57 mg·kg−1) nearly 6 times greater than that of the original QS (232.56 mg·kg−1). Adsorption experiments at different pH showed that the adsorption capacity of ZnAl-LDHs@QS gradually increased as acidity decreased. High-throughput sequencing revealed that the relative abundance of chrome-tolerant microorganisms at the phylum and family levels were increased in modified QS compared with original QS. Hemocytometer counting revealed enhanced microbial quantity on the surface of QS after modification. The content of extracellular polymeric substances (EPS) and the enzymatic activity of the microorganisms adhered to the surface of modified and original QS were detected, results showed that Al-LDHs had an obvious influence on the promotion of EPS secretion and enhanced the enzymatic activity of microorganisms. These changes indicated that the modified QS created better conditions for microorganism growth, and the improved microbial effect caused strong biosorption, resulting in greatly enhanced Cr(VI) removal. Thus, ZnAl-LDHs@QS is a better choice for CRIS to remove Cr(VI).

Removal efficiency and pathways of phosphorus from wastewater in a modified constructed rapid infiltration system

This study investigated the removal of phosphorus in a modified constructed rapid infiltration system (CRIS). The mechanism of phosphorus removal in the CRIS was studied from the perspective of enzymes, the microbial communities, and their metabolic functions. When the chemical oxygen demand (COD) concentration in the influent was increased from 550 to 650 mg/L to about 1100 mg/L, the total phosphorus (TP) removal efficiency increased, with an effluent TP concentration of about 0.16 mg/L in the CRIS. The matrix in the column contained iron and aluminium elements, which reacted with phosphate in the wastewater, resulting in phosphorus precipitation and, consequently, phosphorus removal. The maximum phosphine production was 1.73 and 0.24 mg/m3 in the matrix and the column ventilator. The alkaline phosphatase activity which had a positive effect on the phosphorus removal was increased in the upper layer of the column. High-throughput sequencing analysis showed that the dominant bacterial phylum in the CRIS was Proteobacteria (49.33–51.8%). The abundance of Dechloromonas in the lower and upper layer of the column was 1.51 and 0.67%. The gene numbers of the phosphatidylinositol signaling system, the phosphonate and phosphinate metabolism, and the phosphotransferase system were 24,468, 10,661, and 20,909 in the upper layer and 27,408, 13,476, and 31,192 in the lower layer of the column.

Cr(VI) removal performance and the characteristics of microbial communities influenced by the core-shell maifanite/ZnAl-layered double hydroxides (LDHs) substrates for chromium-containing surface water

Biological mechanisms for Cr(VI) removing induced by ZnAl-LDHs coated on maifanite substrate were explored in constructed rapid infiltration systems (CRIS). Characteristics of maifanite/ZnAl-LDHs and natural maifanite by scanning electron microscope (SEM) and X-ray fluorescence spectrometer (XRF) confirmed the feasibility of the LDHs coating way. The purification experiments showed that the CRIS with maifanite/ZnAl-LDHs substrate displayed higher Cr(VI) removal performance induced by microorganism than that with natural maifanite. High throughput sequencing results of microorganism immobilized on the two substrates revealed that Methyloversatilis, Novosphingobium, Dongia and Paludibaculum were more abundant in maifanite/ZnAl-LDHs. We conclude that maifanite/ZnAl-LDHs adsorbed more Cr(VI) than natural maifanite, ZnAl-LDHs and the high Cr(VI) concentration ambient of maifanite/ZnAl-LDHs enhanced enzymatic activities and altered microbial community, which leading to higher Cr(VI) removal performance in turn. The present study may provide essential information for exploring whether the LDHs coated on natural substrate will affect the microorganism in CRIS.

Efficiency and mechanisms of cadmium removal via core-shell zeolite/Zn-layer double hydroxides

To investigate the removal mechanisms of cadmium (Cd) by Zn-layer double hydroxides-modified zeolites substrates in constructed rapid infiltration systems (CRIS), the ZnAl-LDHs and ZnFe-LDHs were synthesized and in-situ coated on the original zeolites through co-precipitation method. The prepared Zn-LDHs-modified and original zeolites were characterized by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) methods, whose results provided the evidences that the Zn-LDHs were successfully coated on the original zeolites. From the results of purification experiments, the average Cd removal rates of ZnAl-LDHs-modified, ZnFe-LDHs-modified and original zeolites were 88.40, 86.00 and 32.52%, respectively; demonstrating that the removal rates of zeolites could significantly improve. Additionally, the modification of Zn-LDHS could enhance the theoretical adsorption ability. According to the results of isothermal adsorption and desorption tests, the desorption rates of Zn-LDHs-modified zeolites were higher than that of original zeolites. Cd adsorption capacity of ZnFe-LDHs-modified zeolites was 1428.57 mg kg−1 and original zeolites was 434.783 mg kg−1. In the adsorption kinetic studies, the pseudo-second-order models were used to well describe the experimental results of Zn-LDHs-modified zeolites, indicating that their adsorption types were attributed to be more stable chemisorption. Besides, the relevant microbial tests also confirmed that microbial enzymatic activity and extracellular polymeric substances (EPS) were significantly promoted on surface of Zn-LDHs-modified zeolites. The contents of EPS on the surface of zeolites were as following: ZnAl-LDHs-modified zeolites (78.58128 μg/g) > ZnFe-LDHs-modified zeolites (71.85445 μg/g) > original zeolites (68.69904 μg/g). Meanwhile, the results of high-throughput sequencing showed that modification by Zn-LDHs improved microbial diversity and relative abundance. The Proteobacteria was the dominant phylum and the Acidobacteria was conducive to Cd removal. Overall, it could be concluded that ZnAl-LDHs-modified zeolites might be applied as an efficient substrate for Cd removal in CRIS.

Hexavalent chromium removal from aqueous solution by adsorption on modified zeolites coated with Mg-layered double hydroxides.

In this study, MgAl-LDHs and MgFe-LDHs were synthesized via co-precipitation method and in situ coated on pre-washed zeolites through dipping process in beaker. The obtained modified zeolites and original zeolites were utilized as substrates of constructed rapid infiltration systems (CRIS) to remove hexavalent chromium (Cr(VI)) in wastewater. Micro-morphology features and chemical composition of zeolites before and after modification were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray fluorescence spectrometer (XRF). The SEM, XRD, and XRF results demonstrated the feasibility of LDHs coated on the surface of the original zeolites. Purification experiments in simulated CRIS showed that the Cr(VI) removal rates of zeolites/MgAl-LDHs increased by 110.03% on average every concentration (0.5-16 mg L-1) compared with the original zeolites under 24-h HRT. The adsorption capacity of zeolites/MgAl-LDHs reached 66.98 mg kg-1 at 32 mg L-1 initial Cr(VI) concentration, which is nearly twice that of the original zeolites (33.24 mg kg-1) and 1.5 times higher than that of zeolites/MgFe-LDHs (42.01 mg kg-1). Isothermal adsorption tests showed that the Freundlich isotherm equations gave better fitting to the adsorption process. And zeolites/MgAl-LDHs showed a best fit with pseudo-second-order model which meant that the adsorption of Cr(VI) by zeolites/MgAl-LDHs was dominated by chemisorption. Thermodynamic parameters showed that the process of adsorption for the three substrates was spontaneous and endothermic intrinsically. Zeolites/MgAl-LDHs also displayed nearly 60% desorption rate with low concentration eluent (0.01 mol L-1 NaCl). Therefore, zeolites/MgAl-LDHs were chosen out as an optimal substrate for removing Cr(VI) from wastewater in CRIS. Graphical Abstract.

Removal of Cd(II) by modified maifanite coated with Mg-layered double hydroxides in constructed rapid infiltration systems

To improve the adsorption performance of Cd(II) by maifanite in constructed rapid infiltration systems (CRIS), Mg-layered double hydroxides (MgAl-LDHs, MgFe-LDHs) are prepared by a co-precipitation method and in-situ coated on the surface of original maifanite. Characterization of the successful LDHs-coating modification is realized by the following: scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Brunauer Emmett Teller (BET). In the purification experiments, the average removal rates of Cd(II) were 97.66% for maifanite/MgAl-LDHs and 97.54% for maifanite/MgFe-LDHs, approximately 11% greater than for the original maifanite. Isothermal adsorption experiments and adsorption kinetic experiments were conducted to explore the Cd(II) adsorption mechanism. The modified maifanite demonstrated a higher Langmuir adsorption capacity and stronger surface bond energies compared to the original maifanite. The adsorption type of Cd(II) by maifanite/Mg-LDHs and original maifanite was monolayer adsorption based mainly on chemical adsorption. Furthermore, the extracellular polymeric substances and dehydrogenase activities of the microorganisms were measured and analyzed to study the effect of microorganisms on the removal of Cd(II) in the test columns. High-throughput sequencing technology was also applied to analyze the composition and diversity of bacterial communities. Based on a simple estimation, the synthesis cost of maifanite/MgAl-LDHs was only ¥ 0.33/Kg. In brief, maifanite/Mg-LDHs is an efficient and economical substrate for a CRIS for Cd(II) removal.

Effects of infiltrator structure and hydraulic loading rates on pollutant removal efficiency and microbial community in a modified two‐stage constructed rapid infiltration systems treating swine wastewater

The treatments of swine wastewater with variable hydraulic loading rates (HLRs) and infiltrator structure were investigated using a modified two‐stage constructed rapid infiltration system (CRIS). Furthermore, microbial community distribution at different HLRs in the CRIS was also analyzed by high‐throughput sequencing. Results indicated that when the HLR was 5.44 cm/day and 10.88 cm/day, the removal rate of chemical oxygen demand (COD) was between 68% and 73%. However, the removal rate of COD dropped to 22.3% when the HLR increased to 16.33 cm/day. Compared to the small CRIS, the removal rate of NH3‐N was stable at about 78% in the large CRIS that had ventilation in the middle of the column. In addition, at HLR 11 cm/day, majority of the taxa detected in the CRIS were assigned to Proteobacteria, Firmicutes, and Bacteroidetes. Anaerobic ammonium oxidation occurred in the middle and lower parts of the columns of CRIS. When the HLR increased to 22 cm/day, the abundance of Planctomycetes decreased from 57.48% to 38.88% in the upper layer of the first column, whereas the abundance of Firmicutes increased from 6.8% to 16.17%. Results showed the microbial community shift was observed at different HLR, influencing the pollutants removal rate. © 2019 American Institute of Chemical Engineers Environ Prog, 38: e13218, 2019

Phosphorus removal and mechanisms by Zn-layered double hydroxide (Zn-LDHs)-modified zeolite substrates in a constructed rapid infiltration system.

This work presents novel materials, ZnFe-LDHs-modified (Zn2+ : Fe3+ molar ratio of 2 : 1 and 3 : 1) and ZnAl-LDHs-modified (Zn2+ : Al3+ molar ratio of 2 : 1 and 3 : 1) zeolites, which were synthesized under alkaline conditions via a co-precipitation method and coated in situ on original zeolites. The as-prepared LDHs-modified zeolites were used as substrates for a constructed rapid infiltration system (CRIS) to conduct purification experiments to investigate the phosphorus removal performance of all types of zeolites. The experimental results showed that the phosphorus removal rates of the Zn-LDHs-modified zeolites reached over 80%, which are superior to that of the original zeolites. Furthermore, isothermal adsorption and adsorption kinetic experiments were conducted to explore the adsorption mechanisms. The theoretical maximumadsorption capacities were efficiently enhanced owing to the Zn-LDHs coating strategy. Especially, that of the ZnFe-LDHs-modified (3 : 1) zeolites reached 434.78 mg kg−1, which is much higher than that of the original zeolites. Meanwhile, according to the fitting results of the adsorption kinetics experiments, it was found that the predominant adsorption type of the original zeolites was converted from intrinsically weak physical adsorption into more stable chemical adsorption by the Zn-LDHs coating. Furthermore, high-throughput sequencing was also exerted to uncover the phosphorus removal mechanism by microorganisms. The obtained results indicate that the relative abundance of Pseudomonas and Dechloromonas, which are closely related to phosphorus removal, effectively increased. Overall, the Zn-LDHs-modified zeolites improved the phosphorus removal performance efficiently and sustainably when applied in CRIS.

Removal of hexavalent chromium ions by core-shell sand/Mg-layer double hydroxides (LDHs) in constructed rapid infiltration system

This study aimed to determine the efficiencies and mechanisms of hexavalent chromium (Cr(VI)) removal with modified sand coated by Mg-LDHs in constructed rapid infiltration system (CRIS). Mg-LDHs (MgAl-LDHs, MgFe-LDHs) were prepared by co-precipitation method and in situ coated onto the surface of original sand. Scanning Electron Microscope (SEM) and X-Ray Fluorescence Spectrometer (XRFS) were used to analyze physicochemical properties of sand/Mg-LDHs composites. Results obtained confirmed the successful LDHs-coating modification. During the purification experiments, the average removal rates of Cr(VI) were 47.62% for sand/MgAl-LDHs, 34.15% for sand/MgFe-LDHs and 11.61% for original sand, respectively. The sand/Mg-LDHs had a higher Langmuir adsorption capacity and desorption capability for Cr(VI) compared to original sand. The adsorption kinetic data of different adsorbents were better described by pseudo-second-order model. Intra-particle diffusion model was also used to elucidate the adsorption mechanism. Moreover, extracellular polymeric substances, biomass and enzymatic activity of microbes on the modified and original sand were testified and analyzed to study microbial effect on Cr(VI) removal in test columns. Through a rough economic estimation, the reagent cost of sand/MgAl-LDHs synthesis was only RMB ¥ 0.24/Kg. It could be concluded that MgAl-LDHs modified sand is an efficient and economical substrate of CRIS for Cr(VI) removal.

Effect of Potassium Chlorate on the Treatment of Domestic Sewage by Achieving Shortcut Nitrification in a Constructed Rapid Infiltration System

A constructed rapid infiltration (CRI) system is a new type of sewage biofilm treatment technology, but due to its anaerobic zone it lacks the carbon sources and the conditions for nitrate retention, and its nitrogen removal performance is very poor. However, a shortcut nitrification–denitrification process presents distinctive advantages, as it saves oxygen, requires less organic matter, and requires less time for denitrification compared to conventional nitrogen removal methods. Thus, if the shortcut nitrification–denitrification process could be applied to the CRI system properly, a simpler, more economic, and efficient nitrogen removal method will be obtained. However, as its reaction process shows that the first and the most important step of achieving shortcut nitrification–denitrification is to achieve shortcut nitrification, in this study we explored the feasibility to achieve shortcut nitrification, which produces nitrite as the dominant nitrogen species in effluent, by the addition of potassium chlorate (KClO3) to the influent. In an experimental CRI test system, the effects on nitrogen removal, nitrate inhibition, and nitrite accumulation were studied, and the advantages of achieving a shortcut nitrification–denitrification process were also analysed. The results showed that shortcut nitrification was successfully achieved and maintained in a CRI system by adding 5 mM KClO3 to the influent at a constant pH of 8.4. Under these conditions, the nitrite accumulation percentage was increased, while a lower concentration of 3 mM KClO3 had no obvious effect. The addition of 5mM KClO3 in influent presumably inhibited the activity of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), but inhibition of nitrite-oxidizing bacteria (NOB) was so strong that it resulted in a maximum nitrite accumulation percentage of up to over 80%. As a result, nitrite became the dominant nitrogen product in the effluent. Moreover, if the shortcut denitrification process will be achieved in the subsequent research, it could save 60.27 mg CH3OH per litre of sewage in the CRI system compared with the full denitrification process.

Enhanced removal performance of Cr(VI) by the core-shell zeolites/layered double hydroxides (LDHs) synthesized from different metal compounds in constructed rapid infiltration systems.

Nine kinds of LDHs were synthesized by the co-precipitation method under alkaline conditions with different combinations of trivalent metal compounds (FeCl3, AlCl3, CoCl3) and divalent metal compounds (CaCl2, MgCl2, ZnCl2), which were then coated in situ on the surface of zeolites to synthesize core-shell zeolites/LDHs composites. The zeolites before and after modification were characterized by SEM and X-ray fluorescence spectrometry. Using the different core-shell zeolites/LDHs and original zeolite substrates, the constructed rapid infiltration systems (CRIS) simulated test columns were set to treat the municipal sewage containing hexavalent chromium, Cr(VI). Isothermal adsorption tests were subsequently performed. The average removal efficiencies of the small-sized zeolites were much higher than those of the large-sized zeolites. For the small-sized zeolites, the Cr(VI) removal performances of the Mg-LDHs- and Al-LDHs-modified zeolite substrates were efficiently enhanced in particular, which could reach over 90%. And the removal rate of core-shell zeolites/ZnAl-LDHs reached 94.5%. Meanwhile, the maximum adsorption capacity of ZnAl-LDHs-modified zeolites could reach 51.0mg/kg, indicating that the adsorption properties could be enhanced by ZnAl-LDHs coating. During the purification experiments, most of the LDHs-modified zeolites maintained their predominant chemical adsorption ability for the removal of Cr(VI). Therefore, the small-sized core-shell zeolites/ZnAl-LDHs composites could be used as potential substrates for the efficient removal of Cr(VI) in CRIS.

Effect of starvation on the nitrification performance of constructed rapid infiltration systems

ABSTRACTThree constructed rapid infiltration (CRI) systems (C1, C2 and C3) were operated under 7, 14 and 21 days of continuous starvation, respectively. The effect of starvation on the ammonia removal efficiency (ARE), nitrite accumulation rate (NAR), bioactivity of nitrifiers and content of extracellular polymeric substances (EPS) was investigated. The results showed that the activity of nitrite-oxidizing bacteria (NOB) was higher than that of ammonia-oxidizing bacteria (AOB) in stabilization periods, leading to a complete nitrification in CRI systems. During starvation periods, the activity decay rates of AOB (kAOB) for C1, C2 and C3 were 0.172 ± 0.008, 0.132 ± 0.009 and 0.128 ± 0.009 d−1, respectively, and those of NOB (kNOB) were 0.159 ± 0.005, 0.152 ± 0.009 and 0.150 ± 0.005 d−1, respectively, implying that kAOB was higher than kNOB in a 7-day starvation period, while showing a contrasting result in a 14- or 21-day starvation period. When resuming wastewater supply, AOB activity as well as the ARE in C1, C2 and C3 gradually restored to their initial levels within 6, 10 and 23 days, respectively. However, NOB activity was unable to fully restore after a 14- or 21-day starvation period, causing the final NAR of C2 and C3 to remain at 25% and 60%, respectively. Furthermore, EPS could be used as the source of carbon and energy for hungry microorganisms to guarantee the metabolic activity of living cells in a starvation environment. These findings could provide a theoretical foundation for operational optimization of CRI systems under starvation conditions.

A Study on Mechanism of Organic Matter Removal in a Three-step Series Constructed Rapid Infiltration System Used for Domestic Wastewater Treatment

This study focused on domestic wastewater in a campus and investigated chemical oxygen demand (COD) removal efficiency and removal mechanism in a wastewater treatment system using three-step series constructed rapid infiltration (CRI). The experimental results indicated that the three-step series CRI system led to COD removal of 79.65%, a value 6% greater than that in a system using conventional CRI. Moreover, the effluent water quality of the three-step series CRI system met the first level criteria A as specified in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB18918-2002). Total organic matter and particulate organic matter in the wastewater were removed in the first compartment of the system by 54% and 83%, respectively. The quantity of aerobic ammonifying bacteria decreased from top to bottom along the compartments in the system, and was obviously higher than in the conventional CRI system. The dehydrogenase activity showed an M-shaped variation pattern in which two peak activity values were observed. The COD removal efficiency showed a very significant correlation with the aerobic bacteria quantity (correlation coefficient r = 0.97), and showed a relatively significant correlation with the dehydrogenase activity (r = 0.64). The biofilm mass and the active biofilm mass showed M-shaped variation patterns, and were obviously higher than in the conventional CRI system. The COD removal efficiency showed a relatively significant correlation with the weight of the active biofilm mass (r = 0.73).