TP Removal Research Articles

Cultivation of Desmodesmus multivariabilis for the Treatment of Cosmetic Wastewater

The discharge of cosmetic wastewater into the wastewater treatment systems has become an environmental concern due to high concentrations of nutrients. The current study explored the phytoremediation potential of Desmodesmus multivariabilis, under mixotrophic growth, to remove total organic carbon (TOC), sulfur (TS), nitrogen (TN), and phosphorus (TP) from cosmetic wastewater (CWW). The CWW was prepared using samples supplied by a local cosmetic production company (two dyes, two hair relaxers, as well as two shampoos and conditioners). The bioremediation potential of D. multivariabilis was tested under four different conditions: raw CWW with 0% CO2 in the aeration stream (i.e., atmospheric air); pre-treated CWW with 0% CO2, 2.5% CO2, and 5% CO2. Control experiments were run in parallel. Under mixotrophic growth, the microalga performed best at 5% CO2 in the pre-treated CWW where TOC, TN, TP, and TS removal of >88%, >98%, >95%, and >90% were measured, respectively. The corresponding biomass (dry weight) was >203 mg/L. Relaxers promoted growth most prominently; however, it was observed that there was significant nutrient removal even in the absence of growth in all experiments. The growth followed Liebig’s Law, displaying three distinct phases (CO2 concentration, CO2 mass transfer, and nutrient limited growth). The results demonstrated the potential for the successful bioremediation of cosmetic wastewater by D. multivariabilis.

Study on city tail water treatment in constructed wetland with straw biochar substrate modified by freeze–thaw cycles

The preparation of biochar is one of the important directions to realize the high-value resource utilization of straw. Constructed wetland (CW) has low cost and high efficiency in treating city tail water. In order to improve the purification rate of CW with straw biochar for city tail water, freeze–thaw cycles (FTCs) modification of straw biochar and the application of FTCs-modified biochar in CW were studied. The relatively optimal modification condition of biochar was eight FTCs. The adsorption of CO 2 on eight FTCs-modified biochar was increased by more than 20%. Biochar modified by eight FTCs was used as the CW substrate to promote denitrification, and the nitrate nitrogen (NO 3 − N) mean removal rate of city tail water was exceeded 85%. The eight FTCs-modified biochar reduced the impact on the electrical conductivity of city tail water. The carbon sequestration rate of eight FTCs-modified biochar reached 55.6%. The research results will be helpful to realize the straw carbon sequestration, improve the performance of biochar and the treatment effect of CW on city tail water. • The modification effect of biochar was the best when the number of FTCs was 8 times. • Eight FTCs modified biochar promoted nitrification in CW with plants. • TP removal rate increment exceeded 15% in CW with FTCs-modified biochar and plants. • The FTCs reduced the soluble components of biochar, so the EC was reduced.

A comprehensive study of biological phosphorus removal systems from economic and environmental perspectives based on the optimization approach

Different biological phosphorus removal systems (BPRSs) are evaluated from economic and environmental perspectives by employing the Taguchi optimization approach for the first time. The BPRSs were simulated and compared in terms of total phosphorus removal efficiency (TP RE) using GPS-X software. Step Bio-P, the most efficient system, was selected for the subsequent environmental and cost analysis. At the optimum condition, the Step Bio-P with a 96.98% TP RE stood at the first rank, followed by the Johannesburg (83.17%)> University of Cape Town (UCT) (79.63%)> anaerobic/anoxic/oxic (A 2 O) (79.31%)> anoxic/oxic (AO) (78.89%)> Bardenpho (70.48%). Marine and freshwater ecotoxicity (59.57%) and freshwater eutrophication (11.84%) received the highest environmental impacts. Construction (77.66%) and amortization (7.3%) caused the maximum cost contributions. The sensitivity analysis revealed that chemical oxygen demand (COD) (17.48%) and TP (9.98%) imposed the maximum effects on the environmental categories. These results can be used as a guideline for wastewater reclamation. • Step Bio-P showed the highest TP removal efficiency (96.98%) • The Taguchi optimization confirmed the role of initial TP on the RE (30.08%) • Marine and freshwater ecotoxicity (59.57%) showed the highest environmental impacts. • Construction possessed the maximum cost contributions (77.66%). • The sensitivity analysis showed the effect of COD and TP on the environmental impacts.

Engineering demonstration of the remediation of urban water using a novel MES enhanced ecological floating bed: From construction to long-term performance

An innovative ecological floating bed coupled with sedimental microbial electrochemical system (ECOFB-MES) was designed for urban water remediation. A demonstration-scale ECOFB-MES of approximately 500 m2 was firstly constructed to perform the remediation of 8040 m2 urban water located in Nanning, Guangxi Zhuang Autonomous Region, China. During one-year operation, the COD, NH4+–N, NO3¯–N and TP concentrations stabilized around 10.3 ± 4.0 mg/L, 0.04 ± 0.02 mg/L, 0.61 ± 0.27 mg/L and 0.12 ± 0.05 mg/L from May 2021 to December 2021. The COD, TN and TP removal loads in April when MESs were connected were 72.47 g/d/m2, 4.26 g/d/m2 and 0.39 g/d/m2, which were 3.6, 15.3 and 2.8 times higher than those in January (open circuit). The average TC removal efficiency of sediment near anode was 36.7 %, which was 2.4 times higher than that of sediment far from anode (15.5 %). The average current of the MESs improved from 0.6 ± 0.1 mA to 32.0 ± 2.9 mA with reducing external resistance gradually, which was responsible for higher TC removal efficiency and lower dissolved oxygen (DO) concentration (7.78 ± 1.35 mg/L), which could enhance nitrogen removal. The MES enhanced the total number of species and the bacteria diversity of polyester fibers and roots in the same coupled system. The dominant functional bacteria such as Pseudomonas, Gemmobacter, Aeromonas and Arthrobacter beneficial for oxygen reduction and nitrogen removal were found on biocathode, and this indicated that biocathode of present system could reduce nitrate mainly through heterotrophic nitrification and aerobic denitrification. Results from the president research indicated that the ECOFB-MES provides a rewarding reference for practical application of polluted urban water remediation.

A novel two-stage process for the effective treatment of swine wastewater using Chlorella sorokiniana AK-1 based algal-bacterial consortium under semi-continuous operation

This study aimed at developing an eco-friendly and effective treatment for swine wastewater (SWW) using a designer microalgae-bacteria consortium. A functional algal bacterial consortium was developed with SWW-derived bacteria and Chlorella sorokiniana AK-1. Light intensity (300 µmol/m2/s) and inoculum size (0.15 and 0.2 g/L for microalgae and bacteria) were optimized. Semi-batch operation treating 50 % SWW resulted in a COD, BOD, TN, and TP removal efficiency of 81.1 ± 0.9 %, 97.0 ± 0.7 %, 90.6 ± 1.6 % and 91.3 ± 1.1 %, respectively. A novel two-stage process with an initial bacterial start-up stage followed by microalgal inoculation was applied for attaining stable organic carbon removal, in addition to satisfactory TN and TP removal. Full strength SWW was treated with this strategy with COD, BOD, TN, and TP removal efficiencies of 72.1 %, 94.9 %, 88 %, and 94.6 %, respectively. The biomass consisted of 36 % carbohydrates, indicating a potential feedstock for biochar production. In addition, the effluent met the standards for effluent discharge in Taiwan.

Integration of MFC reduces CH4, N2O and NH3 emissions in batch-fed wetland systems

The combination of microbial fuel cells (MFCs) with constructed wetlands (CWs) for enhancing water purification efficiency and generating bioelectricity has attracted extensive attention. However, the other benefits of MFC-CWs are seldom reported, especially the potential for controlling gaseous emissions. In this study, we have quantitatively compared the pollutant removal efficiency and the emission of multiple gases between MFC-CWs and batch-fed wetland systems (BF CWs). MFC-CWs exhibited significantly (p < 0.01) higher COD, NH4+-N, TN, and TP removal efficiencies and significantly (p < 0.01) lower global warming potential (GWP) than BF CWs. The integration of MFC decreased GWP by 23.88% due to the reduction of CH4 and N2O fluxes, whereas the CO2 fluxes were slightly promoted. The quantitative PCR results indicate that the reduced N2O fluxes in MFC-CWs were driven by the reduced transcription of the nosZ gene and enhanced the ratio of nosZ/(nirS + nirK); the reduced CH4 fluxes were related to pomA and mcrA. Additionally, the NH3 fluxes were reduced by 52.20% in MFC-CWs compared to BF CWs. The integration of MFC promoted the diversity of microbial community, especially Anaerolineaceae, Saprospiraceae and Clostridiacea. This study highlights a further benefit of MFC-CWs and provides a new strategy for simultaneously removing pollutants and abating multiple gas emissions in BF CWs.

Enhanced Treatment of Decentralized Domestic Sewage Using Gravity-Flow Multi-Soil-Layering Systems Coupled with Iron-Carbon Microelectrolysis

Soil-based decentralized treatment technology has become increasingly popular as an ideal solution for water pollution control in rural areas. It is very necessary to optimize the removal mechanisms and performance of such technologies on rural domestic sewage treatment. This was the first study of a gravity-flow multi-soil-layering (MSL) system coupled with iron-carbon microelectrolysis (ICM). Influent COD/TN (C/N) ratio and bottommost soil mixture block (SMB) submersion were selected as the operating factors relevant to the ICM in MSL systems. Such two key factors were investigated in the factorial experiment. The removal efficiencies of COD, TP, NH3-N, NO3−-N, and TN could be reached up to 96.3, 100, 95.4, 93.8, and 79.6%, respectively. Different levels of factors could comprehensively drive the performance variation. The factorial analysis indicated that the bottommost SMB submersion had the most significant and dominant negative effects on aerobic processes. The ideal TP removal attributed to the presence of the bottommost SMB submersion. It played the dominant role for the bottommost SMB submersion in facilitating an electrochemical reaction through the ICM. Zero-valent iron or ferrous ions could be transformed to final ferric ions more efficiently during the period of the ICM reactions. The ICM could promote the capability of a SMB for removing nutrients in sewage, especially provide electron donors to denitrifying bacteria in MSL systems. However, there were non-significant effects of the influent C/N ratio on the removal performance of MSL systems. This study can help enrich the pollutant removal mechanisms in MSL systems.

A novel bio-flocculation combined with electrodialysis process: Efficient removal of pollutants and sustainable resource recovery from swine wastewater

High organic matter load and nutrient concentration in swine wastewater could lead to soil and water pollution by inappropriate land irrigation. To solve the above problem, this study developed an eco-friendly bio-flocculation combined with electrodialysis (BF-ED) process, in which BF could effectively reduce the probability of ED membrane fouling and replaced subsequent biochemical treatment by ED process. High removal of TS (100 %), TP (100 %), and COD (95.68 %) from raw swine wastewater could be obtained via BF pretreatment, while high recovery efficiency of nutrient ions (98.8 % K+ and 84.3 % NH3-N) was achieved after ED process. Besides, dissolved organic matter was effectively removed after BF treatment, which was beneficial to reduce membrane fouling of ED reactor. Nutrient ions recovery from swine wastewater could be used as agricultural fertilizers. The proposed approach not only solve the problem of swine wastewater purification, but also realize the environmentally sustainable swine wastewater.

Mechanism of Fe-C micro-electrolysis substrate to improve the performance of CW-MFC with different factors: Insights of microbes and metabolic function.

Constructed wetland-microbial fuel cell (CW-MFC) is a novel technology for wastewater treatment with electrical generation. This work proposed a Fe-C micro-electrolysis substrate (Fe-C) with biomass modified ceramsite to enhance pollutants removal and electricity generation. The key influencing factors were revealed, and the COD, NH4+-N, and TP removal efficiency was respectively increased by 10.2, 8.1 and 8.78% with 76% higher power output at optimal conditions (e.g. OLR 52.5g/(m2.d), HRT 48h, and aeration rate 800mL/min). Fe-C based substrates improved the microenvironments in CW-MFC, including dissolved oxygen (DO) and oxidation-reduction potential (ORP) lowering and electron transfer facilitation. These contributed to the enrichment of critical microorganisms and metabolic activities. The abundance of functional bacteria (i.e. Geobacter, Thauera and Dechloromonas) were evidently increased. Additionally, the energy metabolism and other functional genes encoding cytochrome c (ccoN), nitrite reductase (nirD) and phosphate transporter (pstA) were all stimulated.

Effects of feeding methods on ecological soil wastewater infiltration systems for sewage treatment

Intermittent feeding method and continuous feeding method were adopted in two experimental form ecological soil wastewater infiltration systems (ESWISs), respectively. The results showed that COD, NH4 + and TN removal efficiencies were enhanced from 81.8%, 70.5% and 45.8% in continuous feeding ESWIS to 90.0%, 88.5% and 72.7% in intermittent feeding ESWIS. The same TP removal efficiency was achieved in two feeding mehtods. Matrix oxidation reduction potential (ORP) was enhanced through the intermittent feeding ESWIS, especially above 60 cm depth of the matrix, which encouraged nitrification. The metabolic activity and reproduction of microbes were improved by intermittent feeding method, such as actinomyces, bacteria, nitrifying bacteria, fungus. Meanwhile, denitrifying bacteria and nitrate reductase (NR), nitrite reductase (NIR) activities were also increased. PCR-DGGE analysis confirmed that intermittent feeding method improved bacterial diversity. These results suggest that intermittent feeding method is viable to heighten the performance of ESWISs in sewage treatment.

Microbial response mechanism of plants and zero valent iron in ecological floating bed: Synchronous nitrogen, phosphorus removal and greenhouse gas emission reduction

Iron-based ecological floating beds (EFBs) are often used to treat the secondary effluent from wastewater treatment plant to enhance the denitrification process. However, the impact and necessity of plants on iron-based EFBs have not been systematically studied. In this research, two iron-based EFBs with and without plants (EFB-P and EFB) were performed to investigate the response of plants on nutrient removal, GHG emissions, microbial communities and functional genes. Results showed the total nitrogen and total phosphorus removal in EFB-P was 45–79% and 48–72%, respectively, while that in EFB was 31–67% and 44–57%. Meanwhile, plants could decrease CH4 emission flux (0–3.89 mg m−2 d−1) and improve CO2 absorption (4704–22321 mg m−2 d−1). Plants could increase the abundance of Nitrosospira to 1.6% which was a kind of nitrifying bacteria dominant in plant rhizosphere. Among all denitrification related genera, Simplicispira (13.08%) and Novosphingobium (6.25%) accounted for the highest proportion of plant rhizosphere and iron scrap, respectively. Anammox bacteria such as Candidatus_Brocadia was more enriched on iron scraps with the highest proportion was 1.21% in EFB-P, and 2.20% in EFB. Principal co-ordinates analysis showed that plants were the critical factor determining microbial community composition. TN removal pathways were mixotrophic denitrification and anammox in EFB-P while TP removal pathways were plant uptake and phosphorus-iron coprecipitation. In general, plants play an important directly or indirectly role in iron-based EFBs systems, which could not only improve nutrients removal, but also minimize the global warming potential and alleviate the greenhouse effect to a certain extent.

Direct Purification of Digestate Using Polymeric Ultrafiltration Membranes: Influence of Materials on Filtration Behavior and Fouling Characteristics.

In-depth exploration of filtration behavior and fouling characteristics of polymeric ultrafiltration (UF) membranes can provide guidance for the selection of materials and the control of membrane fouling during the purification of digestate. In this study, four types of polymeric membranes, (polyethersulfone (PES), polysulfone (PS), polyvinylidene fluoride (PVDF), and polyacrylonitrile (PAN)), were employed to filter digestate from swine manure. The results showed that the viscosity of the digestate dropped from 45.0 ± 11.3 mPa·s to 18.0 ± 9.8 mPa·s, with an increase in temperature from 30.0 °C to 45.0 °C. The four membrane fluxes all increased by more than 30%, with the cross flow velocity increasing from 1.0 m s−1 to 2.0 m s−1. During the batch experiments, the flux maintenance abilities of the membranes were in the order: PAN > PS > PVDF > PES. There were no significant differences in the effects of membrane materials on the removal of COD, TN, and TP (p < 0.05). For UV254 removal efficiency, PS showed the highest efficiency (68.6%), while PVDF showed the lowest efficiency (63.4%). The major fouling type was irreversible hydraulic fouling, and the main elements of scaling were C, O, S, and Ca. Pseudomonadales were the dominant bacteria in the PS (26.2%) and in the PVDF (51.4%) fouling layers, while Bacteroidales were the dominant bacteria in the PES (26.8%) and in the PAN (14.7%) fouling layers. The flux recovery rates (FRRs) of the cleaning methods can be arranged as follows: NaClO > NaOH > Citric acid ≈ Tap water. After NaClO cleaning, the PVDF membrance showed the highest FRR (73.1%), and the PAN membrane showed the lowest FRR (30.1%).

Performance evaluation of vertical constructed wetland units with hydraulic retention time as a variable operating factor

The current research intends to assess the impact of shorter hydraulic retention time (HRTs) and different sized filter material on the pollutant removal performance of two pilot-scale vertical sub-surface flow constructed wetlands (VSSF CW) to treat dairy wastewater. Two CWs (CW-1 & CW-2) were filled with 10 and 20 mm gravels, respectively, planted with Arundo donax, and operated at three different HRTs for treating dairy farm wastewater viz. 6, 12, and 24 h. Over three months, the effluent was tested for TSS, BOD5, TP, and NH4–N removal using standard procedures at regular intervals. Average concentrations of TSS, BOD5, TP, and NH4–N at the final outlets CW-1 and CW-2 were recorded in the range of; TSS: 44.7–118.7 mg L−1, BOD5: 8.1–33.9 mg L−1, TP: 13.7–22.2 mg L−1and NH4–N: 9.1–11.4 mg L−1, respectively. The highest removal of TSS (81.2%), BOD5 (90.2%), TP (65.1%), and NH4–N (82.5%) from wastewater was seen after a 12 h HRT, whereas maximum DO rise (579.0%) was reported after a 6 h HRT in 20 mm gravel-filled CW units. Short HRTs of 6, 12, and 24 h were found to be effective in removing all pollutants from wastewater and maintaining a constant treatment throughout the evaluation period. Results suggest that VSSF CW systems can be operated efficiently under short HRTs while still effectively removing contaminants from dairy wastewater.

La–Fe magnetic bentonite stimulated denitrifying phosphorus removal from low C/N wastewater in the A2/O process: Performance, microbial community, and potential mechanism

A novel process combined A2/O bioreactor with a millimeter-sized magnetic lanthanum-modified bentonite (La–Fe-MB) granules material (terms as A2/O–La–Fe-MB) was proposed for highly efficient phosphorus removal from municipal sewage. A series of experiments were carried out to explore the feasibility and suitability of using La–Fe-MB as a novel adsorbent. The performance of nutrient removal and microbial composition, and any adverse effect brought by dosing La–Fe-MB are of interests. The long-term operation (240 days) suggested that dosing La–Fe-MB in the A2/O bioreactor achieved a highly-efficient TP removal with average effluent TP concentrations for 0.22 mg/L by enhancing denitrifying phosphorus removal (DPR) and chemical precipitation. Based on the mass balance equations, La–Fe-MB contributed to ∼39.7% of TP removal via adsorption/precipitation in the anaerobic zone, 43.6% of TP was removed through anoxic DPR in the anoxic zone, and post-aerobic zone further reduced ∼14.4% of phosphorus. Moreover, an interesting synergic effect between the La–Fe-MB and functional bacteria was found in the combined process. La–Fe-MB addition not only have less effect on the removal of organic, nitrogen species, and functional bacteria (AOB, NOB, etc.,), but significantly facilitated the enrichment of denitrifying phosphorus accumulating organisms (DPAOs) via releasing traces of Fe (Fe(II)/Fe(III)) in bioreactor. Besides, DPAOs (1.7%), glycogen accumulating organisms (GAOs) (0.031%) and P-accumulating organisms (PAOs) (0.41%) co-existed in this combined system, potentially resulting in simultaneous denitrifying dephosphatation and aerobic phosphorus absorbing. The above results demonstrated that the novel A2/O–La–Fe-MB system is a promising technique for highly-efficient TP removal from wastewater.

Study on the effect of ratio of microalgae Chlorella sp. and activated sludge to remove nutrients and organic matter for low C/N wastewater

Microalgae and activated sludge were co-cultured in photobioreactor (PBR) systems with different ratios (1:0, 3:1, 1:1, 0:1 wt/wt) to determine an optimal ratio for organic matter and nutrient removal. The results showed that the PBR systems at 1:0 and 3:1 ratios have higher total nitrogen (TN) removal rates than at two others. The highest TN removal at the ratio of 1:0 achieved 96% and at the ratio 3:1 achieved 90% after six days of operation. In addition, the single-microalgae culture and co-culture microalgae-activated sludge systems had higher TP removal than that in the single-activated sludge one. The highest TP removal of 98.8% was achieved at 1:0 ratio after nine days. The 3:1 and 1:1 ratios had significantly higher COD removal rates than the other ratios with 131 mg/l/d and 118 mg/l/d, respectively. After four days of operation, the 3:1 ratio reached the highest specific removal rate of 132.7 mg/l/d. This study showed that the 3:1 ratio of microalgae co-culture and activated sludge is an optimal ratio for wastewater treatment-based microalgae application.

The pollutant elimination performance and bacterial communities of unpowered baffle rural sewage reactor filtered with construction wastes

Sewage and construction waste in rural areas are urgently needed to be effectively treated with low cost as the higher environmental demand and lower economic level in rural areas. In this study, unpowered baffle rural sewage reactors filtered with different construction wastes, autoclaved aerated concrete (ALC), composite mortar (CM), and red brick (RB), were established and operated to achieve the cooperative governance of rural sewage and rural construction wastes. The pollutant removal effect and bacterial communities were revealed and the mechanism of pollutant removal caused by construction wastes was discussed. Unpowered baffle rural sewage reactors filtered with construction wastes had evident removal effect on COD (31.57%–55.07%) and SS (27.57%–41.36%) during the 3 h retention time and cement based construction wastes (ALC and CM) showed evident TP removal effect (16.71%–35.26%). The bacterial communities of construction wastes (e.g. Chlorobium, Comamonas, and Acinetobacter) were complex and differed with waste type. However, the pollutant removal related functions of the bacteria on different construction wastes were similar. The different pollutant removal effect of construction wastes was mainly caused by their physicochemical characteristics, but not their bacterial community characteristics. ALC and RB can be used to COD removal, CM can be used to SS removal, and ALC and CM can be used to TP removal in rural sewage treatment. Overall, this study provided an effectively and low-cost method to co-governance of rural sewage and rural construction wastes which is suitable for rural areas and has development potential.

Microalgal-bacterial consortia for efficient wastewater treatment: Optimization using response surface methodology.

The performance of microalgal-bacterial consortia in wastewater treatment and biomass production needs to be further optimized to meet increasingly stringent effluent standards and operating costs. Besides, due to uncontrollability of ambient conditions, it is generally believed that operating conditions (e.g., aeration) respond to ambient conditions (e.g., illumination). Therefore, response surface methodology (RSM) based on Box-Behnken design was used in this study to analyze the removal of chemical oxygen demand (COD), NH3 -N and TP, and algal biomass of the microalgal-bacterial consortia within 48 h. The results showed that under medium illumination intensity (5000 lx), photoperiod (12:12) and aeration rate (0.55 L min -1 ), the removal efficiency of COD, NH3 -N and TP was the highest, and the maximal biomass growth rates were 95.43%, 95.49%, 89.42% and 99.63%, respectively. However, as the limited critical removal requirements of TP, the effluent standards can only be achieved within the small illumination intensity and photoperiod available range, even under medium aeration conditions, which means that under fixed operating conditions, the effective operation range will be very limited. In addition, based on RSM and differential equation analysis, the further study indicated that the effective treatment range can be greatly expanded within aeration responding, which meets the discharge standard of pollutants in China. PRACTITIONER POINTS: Illumination was responded by aeration for optimizing performance of microalgal-bacterial consortium for wastewater treatment and biomass productivity. The strategy of optimization was based on response surface methodology. The maximum effect on wastewater treatment and biomass productivity was based on partial differential equations and quadratic inhomogeneous equations. Limited to critical TP-removal requirements, effluent standards can meet only in the small-usable range of illumination, under medium aeration.

Fast granulation of flocculent activated sludge by mycelium pellet and wastewater biological treatment performance

To investigate the universality of mycelium pellet (MP) assisted flocculent activated sludge (FAS) granulation, four different filamentous microbes (Aspergillus niger, Aspergillus fumigatus, Phanerochaete Chrysosporium and Streptomyces albicans) were used for bio-flocculation assisted activated sludge granulation, and the physicochemical properties and biological activity of aerobic granular sludge (AGS) with MP as skeleton were monitored. The results showed that inoculation of MP for an assisted flocculation strategy was better than filamentous spores. Spherical and rod-shaped microbes of FAS alternately adhered to different areas of the MP to form granular sludge with dense structure. Under the optimized conditions, the FAS biomass aggregated on four MPs reached 1.24–1.89 g/g, and the respiratory activity of corresponding MP-based AGS (MP-AGS) were 36.52–56.95 mgO2/gVSS of specific oxygen consumption rate. Compared to FAS, MP-AGS present better sedimentation performance (45–55 m/h of settling rate) and higher biological enzyme activity related to organic matter degradation and nitrogen conversion (49.82–60.37 mgTF/(gVSS∙h) of dehydrogenase, 0.26–0.42 mgNO2−-N/(min∙mg protein) of nitrate reductase). TN and TP removal efficiencies of MP-AGS were 9.96 %–19.59 % higher than those of FAS under high influent loads. This study confirmed the feasibility of mycelium pellet assisted flocculent activated sludge granulation using different microbes.

Performance enhancement and population structure of denitrifying phosphorus removal system over redox mediator at low temperature

The development of denitrifying polyphosphate accumulating organisms (DPAOs) presents a strategy to carbon competition between denitrifying bacteria and phosphorus removing bacteria. However, low temperature inhibits the rate of enzyme-catalyzed and substrate diffusion during denitrifying phosphorus removal (DPR). Therefore, the present study assessed the addition of NQS (100 μmol/L) for enhancing the removal of TP and TN in DPR reactors operated at alternating anaerobic and anoxic phases and different influent phosphate concentrations. The results showed that the removal efficiency of TP and TN in NQS-DPR system at 10 °C were 99.9% and 42.0%, respectively, which were 2.1 and 2.0 times higher than that of DPR system. Adding NQS significantly alleviated the increase of pH under anoxic condition and decreased the ORP value of the reactor, which in turn enhanced the PHAs accumulation process. The determination of functional genes (nirK, narG and phoD) showed that Dechloromonas, Lentimicrobium, and Terrimonas were the dominant functional bacteria in NQS-DPR system at 10 °C with the relative abundance of 3.09%, 2.99% and 2.28%, respectively. This study can provide valuable information for the effects of the addition of the redox mediator on denitrifying phosphorus removal technology.

Effect of intermittent operation and shunt wastewater on pollutant removal and microbial community changes in subsurface wastewater infiltration system

Subsurface wastewater infiltration system (SWIS) is widely used in the treatment of rural domestic sewage. However, the nitrogen removal effect is unsatisfactory. In this study, laboratory-scale SWIS was built, and the nitrogen removal capacity of the system was optimized by a combination of intermittent operation and the shunt method. The optimal total nitrogen (TN) removal rate (56.53%) is obtained when the wet-dry ratio (Rwd) is 1:2 and the shunt ratio is 3:1. The optimal ammonia nitrogen (NH4+-N) removal rate (54.97%) is obtained when Rwd is 1:3 and shunt ratio is 2:1. In addition, SWIS achieved a good COD removal rate (>75%) and TP removal rate (>95%) during the whole operation stage. Proteobacteria, Acidobateria and Bacteroidetes are high abundance phyla in SWIS. Bacteroidetes, Chloroflexi and Nitrospirae associated with nitrogen removal are abundant at the shunt ratio of 2:1 and 3:1. At the genus level, Bosea, Bradyrhizobium and Phenylobacterium were functional genera associated with denitrification, enriching the substratum of SWIS at shunt ratios of 1:1, 2:1 and 3:1. Nitrogen (N) forms and ORP analysis showed that under the appropriate shunt ratio and Rwd, the SWIS matrix has a suitable redox microenvironment, and thus creates a well-defined nitrification area and denitrification area. This research provides a reliable theoretical basis for the construction and operation of SWIS in rural areas.