Long-Term Trends in Water Quality Indices in the Lower Danube and Tributaries in Romania (1996-2017)

The Danube River is the second longest in Europe and its water quality is important for the communities relying on it, but also for supporting biodiversity in the Danube Delta Biosphere Reserve, a site with high ecological value. This paper presents a methodology for assessing water quality and long-term trends based on water quality indices (WQI), calculated using the weighted arithmetic method, for 15 monitoring stations in the Lower Danube and Danube tributaries in Romania, based on annual means of 10 parameters for the period 1996–2017. A trend analysis is carried out to see how WQIs evolved during the studied period at each station. Principal component analysis (PCA) is applied on sub-indices to highlight which parameters have the highest contributions to WQI values, and to identify correlations between parameters. Factor analysis is used to highlight differences between locations. The results show that water quality has improved significantly at most stations during the studied period, but pollution is higher in some Romanian tributaries than in the Danube. The parameters with the highest contribution to WQI are ammonium and total phosphorus, suggesting the need to continue improving wastewater treatment in the studied area. The methodology and the results of the study may be very useful instruments for specialists and decision makers in updating river basin management plans and prioritising intervention measures.

Desalination of Municipal Wastewater Using Forward Osmosis

Membrane technology has gained much ground in water and wastewater treatment over the past couple of decades. This is timely, as the world explores smart, eco-friendly, and cheap water and wastewater treatment technologies in its quest to make potable water and sanitation commonplace in all parts of the world. Against this background, this study investigated forward osmosis (FO) in the removal of salts (chlorides, sulphates, and carbonates) and organics (chemical oxygen demand (COD), turbidity, total suspended solids (TSS), and color) from a synthetic municipal wastewater (MWW), mimicking secondary-treated industrial wastewater, at very low feed and draw solution flow rates (0.16 and 0.14 L/min respectively), using 70 g/L NaCl solution as the draw solution. The results obtained showed an average of 97.67% rejection of SO₄²⁻ and CO₃²⁻ while Cl⁻ was found to enrich the feed solution (FS). An average removal of 88.92% was achieved for the organics. A permeation flux of 5.06 L/m².h was obtained. The kinetics of the ions transport was studied, and was found to fit the second-order kinetic model, with Pearson’s R-values of 0.998 and 0.974 for Cl⁻ and CO₃²⁻ respectively. The study proves FO as a potential technology to desalinate saline MWW.

Biogas production by co-digestion of municipal wastewater and food waste: Performance in semi-continuous and continuous operation

Municipal wastewater has recently attracted interest in relation to anaerobic wastewater treatments. Biogas production with co-digestion of mixed substrates has been proposed and has many potential benefits for municipal wastewater. The aim of this research was to assess the performance of biogas production during co-digestion of municipal wastewater and food waste under semi-continuous and continuous operation with various hydraulic retention times (HRTs). A laboratory-scale continuous stirred tank reactor (CSTR) at room temperature operation (27-32°C) was employed in this research. The highest methane yields of 167.41 ± 66.52, 194.35 ± 85.44, and 214.81 ± 85.44 ml/g-Vs were found in semi-continuous mode, respectively, at 30, 10, and 10 days of HRTs with a 10:90 ratio of municipal wastewater to food waste (based on TS). Result finding of optimum condition (10 days of HRTs) presented a methane yield of 485.58 ± 82.35 ml/g with continuous operation. Hence, food waste has practical implications for use as a co-substrate with the optimization condition of HRT and operation mode for biogas production from municipal wastewater. PRACTITIONER POINTS: Food waste has good potential for use as a co-substrate for biogas production from municipal wastewater. HRT reduction from 30 to 10 days in semi-continuous, biogas production from municipal wastewater and food waste increased by 59%. Co-digestion of municipal wastewater and food waste with continuous mode and 10 days of HRT was the effective biogas production.

Microalgae based wastewater treatment: a shifting paradigm for the developing nations

Decreased water quality in freshwater resources due to untreated or partially treated wastewater disposal resulting in eutrophication has led to water scarcity. Hence, the present work was aimed to determine the effectiveness of Chlorella vulgaris for municipal wastewater treatment in terms of various physico-chemical parameters and nutrient removal. Primary treated effluent was collected from a sewage treatment plant as an influent for the study. Parameters analyzed during the lab-scale batch study of 7 hours of detention time were pH, EC, TDS, TSS, TS, COD, phosphate, ammonia, nitrate and DO. Removal efficiency reached 98.32, 97.26 and 84.71% for phosphate, ammonia and COD, respectively, for non-filtered effluents. However, filtered effluent removal efficiency reached 98.53, 98.63 and 89.41% for phosphate, ammonia and COD, respectively. The study revealed that microalgal treatment, if incorporated in conventional wasteater treatment, can be a solution to the limitations of the activated sludge process. It could be a promising technique for low income and developing countries, which could efficiently reduce the effluent concentration to much lesser than the desirable limits in an eco-friendly and cost-effective way. Statement of novelty Municipal wastewater treatment in most developing countries is confined to aerobic secondary treatments, which are costly and are not efficient in removing nutrients from the treated effluents before discharging and leading to the imbalance and eutrophication in the receiving bodies. Hence in this study, an attempt was made to study the effectiveness of Chlorella vulgaris for wastewater treatment at a detention time of 7 hours without any external aeration. The present study revealed that microalgae have efficiently removed organics and nutrients to much lesser than the desirable limit. Thus, if the Chlorella vulgaris is introduced in the wastewater treatment system can reduce the nutrients and organics concentrations without the need for aeration, which can be an energy-saving and cost-effective approach.

Membrane Bioreactor Technology: The Effect of Membrane Filtration on Biogas Potential of the Excess Sludge

Although the membrane bioreactor technology is gaining increasing interest because of high efficiency of wastewater treatment and reuse, data on the anaerobic transformations of retentate are scarce and divergent. The effects of transmembrane pressure (TMP) in microfiltration (MF) and ultrafiltration (UF) on the pollutant rejection, susceptibility of ceramic membrane to fouling, hydraulic parameters of membrane module, and biogas productivity of retentate were determined. Irrespective of the membrane cut-off and TMP (0.2-0.4 MPa), 97.4 ± 0.7% of COD (chemical oxygen demand), 89.0 ± 4.1% of total nitrogen, and 61.4 ± 0.5% of total phosphorus were removed from municipal wastewater and the permeates can be reused for irrigation. Despite smaller pore diameter, UF membrane was more hydraulically efficient. MF membrane had 1.4-4.6 times higher filtration resistances than UF membrane. In MF and UF, an increase in TMP resulted in an increase in permeate flux. Despite complete retention of suspended solids, strong shearing forces in the membrane installation changed the kinetics of biogas production from retentate in comparison to the kinetics obtained when excess sludge from a secondary clarifier was anaerobically processed. MF retentates had 1.15 to 1.28 times lower cumulative biogas production than the excess sludge. Processing of MF and UF retentates resulted in about 60% elongation of period in which 90% of the cumulative biogas production was achieved.

Hydrolysis and Methanogenesis in UASB-AnMBR Treating Municipal Wastewater Under Psychrophilic Conditions: Importance of Reactor Configuration and Inoculum

Three upflow anaerobic sludge blanket (UASB) pilot scale reactors with different configurations and inocula: flocculent biomass (F-UASB), flocculent biomass and membrane solids separation (F-AnMBR) and granular biomass and membrane solids separation (G-AnMBR) were operated to compare start-up, solids hydrolysis and effluent quality. The parallel operation of UASBs with these different configurations at low temperatures (9.7 ± 2.4°C) and the low COD content (sCOD 54.1 ± 10.3 mg/L and pCOD 84.1 ± 48.5 mg/L), was novel and not previously reported. A quick start-up was observed for the three reactors and could be attributed to the previous acclimation of the seed sludge to the settled wastewater and to low temperatures. The results obtained for the first 45 days of operation showed that solids management was critical to reach a high effluent quality. Overall, the F-AnMBR showed higher rates of hydrolysis per solid removed (38%) among the three different UASB configurations tested. Flocculent biomass promoted slightly higher hydrolysis than granular biomass. The effluent quality obtained in the F-AnMBR was 38.0 ± 5.9 mg pCOD/L, 0.4 ± 0.9 mg sCOD/L, 9.9 ± 1.3 mg BOD₅/L and <1 mg TSS/L. The microbial diversity of the biomass was also assessed. Bacteroidales and Clostridiales were the major bacterial fermenter orders detected and a relative high abundance of syntrophic bacteria was also detected. Additionally, an elevated abundance of sulfate reducing bacteria (SRB) was also identified and was attributed to the low COD/SO₄ ^2- ratio of the wastewater (0.5). Also, the coexistence of acetoclastic and hydrogenotrophic methanogenesis was suggested. Overall this study demonstrates the suitability of UASB reactors coupled with membrane can achieve a high effluent quality when treating municipal wastewater under psychrophilic temperatures with F-AnMBR promoting slightly higher hydrolysis rates.

[Competitive Selection of Hydroxylamine on Ammonia Oxidizing Bacteria and Nitrite Oxidizing Bacteria]

The effective inhibition of nitrite oxidizing bacteria (NOB) is the key to realizing satisfactory nitrite accumulation and achieving effective nitritation. In order to explore the selective effect of hydroxylamine (NH₂ OH) on ammonia oxidizing bacteria (AOB) and NOB, a sequencing batch reactor (SBR) with the operation mode of anaerobic/aerobic/anoxia (A/O/A) was used to observe the start-up of nitritation at different concentrations and frequencies of NH₂ OH. The results showed that when 5 mg·L^-1 of NH₂ OH was added once every 2 cycles, the nitrite accumulation rate (NAR) increased from 0.1% to 57.4% in 6 days, and was maintained at (62.0±4.6)% until the end of the trials. In the typical cycle on day 6, the NN₄⁺-N dropped from 26.05 mg·L^-1 to 8.06 mg·L^-1, thus producing 9.02 mg·L^-1 of NO₂^--N and 6.70 mg·L^-1 of NO₃^--N. Meanwhile, the ratio of the maximum activity of AOB (rAOB) to NOB (rNOB) increased from 1.05 on day 1 to 4.22 on day 9. Moreover, qPCR results indicated that the abundance of AOB and NOB decreased to 30.2% and 19.1%, respectively, on day 9 in comparison to the original sample. The results indicate that the selective effect of AOB and NOB based on NH₂ OH is expected to provide a feasible application for the rapid start-up nitritation of municipal wastewater.

Forward osmosis with an algal draw solution to concentrate municipal wastewater and recover resources

This study aimed to concentrate and recover resources from municipal wastewater with a novel forward osmosis (FO) system. The FO system used synthetic seawater as the draw solution (DS) to extract water from the feed solution (FS) (synthetic raw municipal wastewater). Because ammonium passed through the FO membrane from the FS to the DS, we cultivated an algal strain (Chlorella vulgaris) in the DS to remove and recover ammonium. For three consecutive FO cycles, the algal FO system removed 35.4% of the ammonium from the DS, increased the concentrations of COD and PO 4 3 - - P in the FS by 43.0%, and achieved a water flux of 11.59 ± 0.49 L m^-2  hr^-1 . Throughout the FO cycles, the algal biomass concentration of the DS stayed at 606 ± 29 mg COD/L due to simultaneous algal growth and DS dilution. This FO process may be feasible to implement for full-scale applications to concentrate wastewater and recover resources. PRACTITIONER POINTS: A novel forward osmosis (FO) system with an algal draw solution (DS) concentrated municipal wastewater and recovered resources (ammonium). Ammonium but not organic matter or phosphate diffused across the FO membrane from the feed solution (FS) to the DS. The algal FO system increased COD/phosphate concentration in the FS by 43.0% and removed 35.4% of ammonium from the DS. The water fluxes in the algal FO system and the control were 11.59 and 12.02 L m^-2  hr^-1 , respectively. The novel algal FO process has the potential to improve full-scale efficiency by concentrating municipal wastewater and recovering nutrients.

[Advanced Nitrogen Removal Characteristics of Low Carbon Source Municipal Wastewater Treatment via Partial-denitrification Coupled with ANAMMOX]

Partial-denitrification coupled with ANAMMOX is a novel biological nitrogen removal technology, which is expected to significantly reduce the external carbon source dosage for advanced nitrogen removal from municipal wastewater. In this study, ANAMMOX sludge was inoculated to investigate advanced nitrogen removal performance and sludge characteristics in a partial-denitrification/ANAMMOX reactor. The results showed that inoculation of ANAMMOX sludge could quickly start the partial-denitrification/ANAMMOX reactor. The effluent total nitrogen concentrations were (4.82±1.84) mg·L^-1 with a chemical oxygen demand of 2.19±0.08. Sludge particles larger than 0.20 mm accounted for 86.16% in the reactor. This meant that granular sludge was formed, which was conducive to good retention of ANAMMOX bacteria in the reactor. The external carbon source dosage and the oxygen requirement for nitrification can be reduced by applying partial-denitrification coupled with ANAMMOX to advanced nitrogen removal from the effluent of secondary clarifier in municipal wastewater treatment plants.

[Effect of Alkaline Sludge Fermentation Products on the Nitrification Process and Performance]

The aim of the present study was to investigate the effect of alkaline sludge fermentation products as a carbon source on the nitrification process and performance. During the operation of a biological nitrogen removal (BNR) system with sludge fermentation mixture as the carbon source, the activities of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were inhibited at the beginning. After 16 days, the activity of AOB began to recover rapidly, but the activity of NOB was still inhibited. The specific nitrate production rate (SNaPR, N/VSS) decreased from 0.1791 g·(g·d)^-1 to 0.0078 g·(g·d)^-1. At the same time, the nitrite accumulation rate increased from 8.12% to 91.42% and remained stable. The sludge fermentation mixture was separated into sludge fermentation liquid and sludge fermentation sediment. The changes in nitrification activity by adding different types of fermentation products were investigated. The results showed that the activity of NOB decreased in the experimental group fed with the sludge fermentation mixture and the fermentation liquid. The SNaPR decreased from an initial 0.1793 g·(g·d)^-1 to 0.1510 g·(g·d)^-1 and 0.1617 g·(g·d)^-1, respectively. In the experimental group fed with fermentation sediment, the activity of NOB increased. SNaPR rose from 0.1793 g·(g·d)^-1 to 0.1864 g·(g·d)^-1. Therefore, the activity of the NOB can be inhibited when the sludge fermentation mixture and the fermentation liquid are used as a carbon source in the nitrification process. In addition, the short-range nitrification process can be realized, which is beneficial to accelerating the reaction speed and saving investment in this type of carbon source.

Kinetic study of nutrients removal from municipal wastewater by Chlorella vulgaris in photobioreactor supplied with CO2-enriched air

The microalgae Chlorella vulgaris ATCC 13482 was used in the present study for municipal wastewater treatment. Batch experiments were performed in bubble column photobioreactors of 7 L working volume maintained at 25 ± 2°C and 14 h/10 h of photo and dark cycle. The treatment process was enhanced by using CO₂-augmented air (5% CO₂ v/v) supply into the microalgal culture in comparison to the use of normal air (0.03% CO₂ v/v). For a period of 7 days, C. vulgaris effected maximum removals of 74.4% soluble fraction of chemical oxygen demand, 72% ammonia (NH₄-N), 60% nitrate (NO₃-N) and 81.93% orthophosphate (PO₄-P) with use of normal air, whereas 84.6% sCOD, 88% NH₄-N, 72% NO₃-N and 92.8% PO₄-P removals, respectively, with use of 5% CO₂/air supply. Using kinetic study data, the specific rates of ammonia and phosphate uptake (q_ammonia and q_phosphate) by C. vulgaris at 5% CO₂/air supply were found to be 2.41 and 0.85 d^-1, respectively. Using the algal remediation technology, nitrogen-phosphorus-potassium recovery from sewage treatment plant of 37.5 million litres per day wastewater influent capacity was calculated to be ∼298.5, 55.4 and 83.7 kg d^-1, respectively.

Quantification and Multidrug Resistance Profiles of Vancomycin-Resistant Enterococci Isolated from Two Wastewater Treatment Plants in the Same Municipality

Wastewater treatment plants (WWTPs) are points of control for the environmental dissemination of antimicrobial resistant bacteria. Vancomycin-resistant enterococci (VRE) were used as indicators of antimicrobial resistance (AMR) in two WWTPs (biologically aerated filter (BAF) and conventional activated sludge (CAS)) in the same municipality. The removal and abundance of enterococci and VRE as well as the species and antimicrobial resistance profiles of VRE were assessed. Enterococci and VRE from the primary and final effluents were enumerated. Results were assessed from an ecological context. VRE was not selected for by either WWTP but the BAF system outperformed the CAS system for the removal of enterococci/VRE. Enterococcus faecalis (n = 151), E. faecium (n = 94) and E. casseliflavus/E. gallinarum (n = 59) were the dominant VRE species isolated. A decrease in levofloxacin resistance in enterococci was observed in the BAF WWTP. An increase in nitrofurantoin resistant (p < 0.001) and a decrease in quinupristin/dalfopristin (p = 0.003) and streptomycin (p = 0.022) resistant enterococci were observed in the CAS WWTP, corresponding to a shift of VRE from E. faecalis to E. faecium. Wastewater treatment processes can be managed to limit the dissemination of antimicrobial resistance determinants into the surrounding environment.

Performance of horizontal sub-surface flow constructed wetlands with different flow patterns using dual media for low-strength municipal wastewater: a case of pilot scale experiment in a tropical climate region

The work presented in this paper is based on the pilot study that was performed to investigate the role of flow pattern in the constructed wetlands (CWs) on the treatment performance of real low-strength municipal wastewater. Four identical pilot-scale horizontal sub-surface flow constructed wetlands (HSSF-CWs) were installed, out of which three beds were planted with a common macrophyte, whereas one was kept as a control. The distinction in the hydraulic design was baffles, vertical up-down (CW2) and side slits (CW3), and the third bed (CW1) was kept horizontal plain type (without baffles). The filter media used in all the beds was dual type, coarse and fine gravel. Monitoring was carried out to determine BOD₅, COD, TSS, NH₄⁺-N, TN, and TP concentrations at different sampling points. Results show that the baffled beds performed better compared to the non-baffled in the order of CW2 > CW3 > CW1 > Control. The highest removal efficiency was measured in the CW2 with a reduction in BOD₅ (86%), COD (77%), TSS (80%), NH₄⁺-N (59%), TN (66%), and TP (64%). The statistical method used also showed that the flow pattern has an impact on the treatment performances of the CWs.

[Advanced Denitrification of Municipal Wastewater Achieved via Partial ANAMMOX in Anoxic MBBR]

Anoxic MBBR is a process to achieve advanced denitrification from municipal wastewater. Here, anoxic MBBR was applied as a post-denitrification SBR to achieve advanced denitrification by partial anammox (anaerobic ammonium oxidation). During a 250-day operation, denitrification performance gradually improved and the total nitrogen concentration of the effluent was approximately 5 mg·L^-1. The average nitrate, ammonia, and total inorganic nitrogen removal efficiencies were (97.7±2.9)%, (93.3±2.9)%, and (94.3±2.7)%, respectively, between day 211 and 250. The simultaneous removal of ammonia and nitrate was observed in the anoxic reactor. Analysis of the ammonia removal pathway revealed that assimilation and nitrification were poor in the anoxic MBBR. The anammox activity test and the denitrification performance showed that anammox occurred and played a not insignificant role in the anoxic MBBR. The results of real-time quantitative PCR showed that anammox bacteria enriched in anoxic MBBR, especially in the anoxic carrier biofilms, where the abundance of anammox bacteria increased from 4.37×10⁷ copies·g^-1 to 2.28×10¹⁰ copies·g^-1. This study demonstrates that anoxic carrier biofilms may have potential applications in anammox bacterial enrichment to enhance denitrification from municipal wastewater.

A new enzymatic method assessing the impact of wastewater treatment plant effluents on the assimilative capacity of small rivers

Microorganisms play an important role in maintaining a good water quality in rivers by degrading organic material, including toxic substances. In the present study, we analyzed the potential impact of municipal wastewater treatment plant (WWTP) effluents as a major stress factor on the assimilative capacity of small rivers. It was the aim to develop a new bioassay for assessing such impacts in the receiving rivers by measuring the activity of extracellular enzymes (exoenzymes) in bacteria. Therefore, we established a specific in-vitro assay to detect inhibitory effects of solid phase-enriched water samples on β-glucosidase (BGL) activity of the actinobacterium Cellulomonas uda as a proxy for the microbial decomposition of organic substances and thus for the assimilative capacity of surface waters. We found significant reductions of BGL activity in the WWTP effluents and in the receiving waters directly downstream as well as a relative quick recovery over the further course of the water bodies. The new bioassay offers a promising tool for the assessment of the assimilative capacity in surface waters and a potential impact of WWTP effluents on this key ecosystem function. Abbreviations WWTP wastewater treatment plant BGL β-glucosidase EU-WFD European Water Framework Directive FAU Formazin Attenuation Units PE population equivalents REF relative enrichment factor; SPE solid phase extraction MTBE methyl-tert-buthyl-ether DMSO dimethyl-sulfoxide NPG 4-nitrophenol-β-d-glucopyranoside DOC dissolved organic carbon.

Efficiency of nitrogen and phosphorus compounds removal in hydroponic wastewater treatment plant

Wastewater treatment with the use of plants is one of the most promising treatment technologies for municipal, domestic and industrial wastewater. The aim of this study was to evaluate the reduction of biogenic compounds concentrations in municipal wastewater treated with the use of hydroponic technology as a tertiary treatment. Research was conducted to assess the suitability of hydroponic lagoon use for municipal wastewater treatment. Samples of sewage for its quality tests were taken from a wastewater treatment plant (WWTP) located in the south-western part of Poland. Average efficiencies of nutrients removal were calculated. Analyses show that the effectiveness of purification is similar for systems with and without the use of the third stage of purification and reached around 82-83% for total nitrogen and 77-79% for ammonium nitrogen. N-NO₂ and N-NO₃ removal efficiency was very low for both analysed systems where for total phosphorus and phosphates it oscillated around 83-84%.

Operation of a modified anaerobic baffled reactor coupled with a membrane bioreactor for the treatment of municipal wastewater in Taiwan

A modified anaerobic baffled reactor (ABR) combined with a submerged membrane bioreactor (MBR) was applied to treat municipal wastewater. The performance of this process was examined in terms of the removal of organic matter, suspended solids, turbidity and nitrogen. The raw wastewater was fed to the 105 L ABR and then the treated effluent was driven to a 58 L MBR equipped with a submerged hollow fibre ultrafiltration membrane module. The integrated modified ABR-MBR process resulted in the complete removal of total suspended solids (TSS) and in very high chemical oxygen demand (COD) removal (93.3 ± 3.8%). Furthermore, the recycling of mixed liquor from the MBR to the modified ABR resulted in some denitrification occurring in the first compartment of the ABR, resulting in 53 ± 6% removal of nitrogen by the integrated process. The membrane flux was stable and above 20 L/m²h. Membrane examination at the nanoscale indicated the deposition of small particles on the surface of the membranes.

[Assessing Performance of Pollutant Removal from Municipal Wastewater by Physical and Chemical Methods Based on Membranes]

The removal characteristics of various pollution factors in municipal wastewater by membrane-based physical and chemical treatment, especially the enrichment characteristics of dissolved organic matter, were investigated by high performance liquid chromatography and three-dimensional fluorescence spectroscopy. The results showed that the municipal wastewater had a low COD/TN ratio after the treatment. The micro-flocculation filtration mainly enriched the non-dissolvable organic matter in the raw water and aromatic protein substances with relative molecular mass greater than 30 000. The enrichment degree was up to 60.93%, especially for tyrosine-like and tryptophan-like substances. The dissolved organic matter (DOM) with a molecular weight greater than 30 000 was enriched fully by 0.45 μm and 0.22 μm acetate membranes, but the microfiltration membrane was not selective for the enrichment of organic matter. Thus, NF mainly enriched the fulvic acid and humic acid in urban sewage. The enrichment degree was 52.01% and 53.57%, respectively, and the total enrichment degree of dissolved organic matter was about 42%.

[Operating Characteristics of a DPR-SNED System Treating Low C/N Municipal Wastewater and Nitrate-containing Sewage]

In order to realize the simultaneous treatment of low C/N municipal wastewater and high nitrate wastewater, a sequencing batch reactor (SBR), inoculated with activated sludge, was used to initiate the denitrifying phosphorus removal coupled with simultaneous nitrification and endogenous denitrification (DPR-SNED). The anaerobic/anoxic/hypoxic durations and dissolved oxygen (DO) concentration were appropriately controlled, and the nitrogen and phosphorus removal characteristics were examined. The experimental results demonstrated that, in the anaerobic/hypoxia operation mode, with an anaerobic duration of 3 h and DO concentration of 0.5-1.0 mg·L^-1, the simultaneous nitrification of phosphorus removal (SNEDPR) system successfully began in 60 d. The effluent PO₄^3--P concentration was below 0.5 mg·L^-1, the nutrient and COD removal efficiencies were stably maintained above 90% and 80%, respectively, and the SNED efficiency and COD_ins efficiency reached 70% and 95%, respectively. When the operation mode was anaerobic/anoxic/hypoxic and nitrate-containing sewage was added at the beginning of the anoxic stage, DPR-SNED was achieved with the effluent PO₄^3--P concentration<0.5 mg·L^-1, nutrient and COD removal efficiencies above 88% and 90%, respectively, and SNED efficiency and COD_ins efficiency maintained at 62% and 90%, respectively. After the successful initiation of DPR-SNED, enhanced intracellular carbons storage was achieved by phosphorus-and glycogen-accumulating organisms using the limited carbons in raw municipal wastewater to provide sufficient carbon sources for subsequent nutrient removal. In addition, the endogenous partial denitrification ensured the efficient nitrogen removal performance of the DPR-SNED system at low C/N conditions (average 4).

Effect of COD/N ratio on denitrification from nitrite

The objective of this study was to investigate dynamic specific denitrification rates (SDNRs) from nitrite at various chemical oxygen demand (COD)/nitrogen (N) ratios using municipal wastewater (MWW). A sequencing batch reactor (SBR) continuously fed with primary effluent and nitrite solution was operated at hydraulic retention time of 8.4 hr and solids retention time of 26-30 days for 3 months. Influent MWW characteristics varied significantly during the study, that is, 200-810 mgCOD/L and 6-80 mgN/L. The SDNRs from the SBR were compared with those determined in four batch reactors using acetate. The SDNR was directly related to COD/N until a maximum SDNR (mgNO₂ -N/mgVSS/day) of 0.07 for MWW and 0.4 for acetate occurred at COD/N ratios of 6 and 13, respectively; beyond this COD/N ratio, SDNR decreased. The biomass yield coefficients (mgVSS/mgCOD) were 0.33 for MWW and 0.51 for acetate. The relationships of SDNR with COD/N and F/M ratios were developed. PRACTITIONER POINTS: The optimum carbon dose for denitrification should be determined using acclimatized biomass. Each carbon source should only be dosed at an optimum that maximizes denitrification.

Heavy metal phyto-accumulation in leafy vegetables irrigated with municipal wastewater and human health risk repercussions

In this study, heavy metal phyto-accumulation potential of selected cultivars of two leafy vegetables on irrigation with municipal wastewater and human health risks were investigated. Municipal wastewater chemistry was recorded significantly different from groundwater control and led to the two-fold high enrichment of soil heavy metal contents (Ni, 19.46; Pb, 23.94; Co, 4.68; Cd, 1.4 in mg/kg, respectively). Interactive effects for phyto-accumulation of most heavy metals were also recorded significant at p < 0.001 in four vegetable cultivars. Heatmap revealed higher accumulation of heavy metals (Fe, Zn, Mn, Cu, Pb, Cr, Co) in spinach cultivars than lettuce cultivars creating elevated health risk index (HRI) and hazard index (HI) values for adults and children. Highest HI was recorded for Lahori palak (adults, 1.42; children, 2.58) and lowest for iceberg (adults, 0.04; children, 0.07). The NPK supplementation improved mineral composition of leafy vegetables within safer human health limits in control treatments. However, in municipal wastewater treatments, NPK fertilization decreased heavy metal uptake and phyto-accumulation in S2 (Lahori palak) than remaining vegetable cultivars leading to reduced health risk values. Because of higher heavy metal phyto-accumulation and health risks, cultivation of spinach cultivars must be discouraged in agro-ecologies receiving municipal wastes, whereas lettuce cultivars should be promoted.

Decentralized wastewater treatment using passively aerated biological filter

This study aimed to evaluate the efficiency of a novel pilot-scale passively aerated biological filter (PABF) as a low energy consumption system for the treatment of municipal wastewater. It consists of four similar compartments, each containing 40% of a non-woven polyester fabric as a bio-bed. The PABF was fed with primary treated wastewater under a hydraulic retention time (HRT) of 3.5 hr and a hydraulic loading rate of 5.5 m²/m³/d. The effect of media depth, HRT, dissolved oxygen (DO) and surface area of the media on the removal efficiency of pollutants was investigated. Results indicated that increasing media depth along the axis of the reactor and consequently increasing the HRT and DO resulted in great removal of different pollutants. A significant increase in the DO levels in the final effluent up to 6.7 mg/l resulted in good nitrification processes. Statistical analysis using SPSS showed that the reactor performance has significant removal efficiency (p < .05) for all pollutants. Overall results indicated that PABF is a viable ecological engineering approach that can be optimized and applied to improve water quality with minimal consumption of energy and low sludge production compared with conventional activated sludge and trickling filter systems.

Treatment efficiency of a hybrid constructed wetland system for municipal wastewater and its suitability for crop irrigation

Design and implementation of wastewater treatment is inevitable due to toxic effects of wastewater irrigation on crops, soil and human health. Current investigation is the pioneer attempt on full-scale hybrid constructed wetland system (HCWS) built for municipal wastewater treatment from Pakistan. HCWS was comprised of vertical sub-surface flow constructed wetland (VSSF-CW) and five phyto-treatment ponds connected in series. Higher environmental risk was associated with untreated municipal wastewater usage in irrigation as estimated through discharge of metals to recipient soils. Treatment efficiency percentages recorded for HCWS reclaimed water quality parameters were, i.e., EC (56.68), TDS (56.86), alkalinity (39.67), chloride (39.68), sulfate (46.73), Na (28.80), Mn (65.24), Cr (78.07), Ni (81.02), BOD (68.74), total hardness (19.56), Fe (70.09), phosphate (55.40), Pb (80.48), COD (63.64), Mg (17.24), K (60.05), Co (100), Cu (67.73), Zn (59.97), Cd (100), and Ca (21.47) respectively. Wastewater treatment in HCWS was due to aquatic plants [Phragmites australis Cav. Trin. ex Steud., Canna indica L. Typha latifolia L., and Hydrocotyle umbellata L.], microbial activities and substrate based wetland processes. The HCWS treated water was well under irrigation standards and recommended for safer crop production in water scarce regions.

[Effect of Denitrification and Phosphorus Removal Microorganisms in Activated Sludge Bulking Caused by Filamentous Bacteria]

Activated sludge bulking or foaming caused by filamentous bacteria is a frequent problem in the operation and management of wastewater treatment plants. To clarify the effect of filamentous bacteria sludge bulking on the functional flora in the biological denitrification and phosphorus removal system, morphological identification and Illumina MiSeq sequencing were applied to investigate the distribution of key micro-flora from the non-bulking period, sludge bulking period, and biological foaming period in five municipal wastewater treatment plants. The results showed that the sludge bulking and biological foaming were caused by Microthrix parvicella when the maximum contents were 6% and 38%, respectively. The main bacteria for denitrification and phosphorus removal were Nitrosomonas, Nitrospira, Thauera, and Candidatus Accumulibacter phosphatis. Compared to the non-bulking period, the relative abundance of AOB and PAO was significantly decreased when the maximum contents were 54% and 47%, respectively, during the bulking period. In addition, the relative abundance of denitrifying bacteria was significantly increased when the maximum content was 73%. The fluctuation of micro-flora for denitrification and phosphorus removal was affected by the activated sludge bulking and was related to the treatment process and physiological characteristics of the bacteria.

[Pilot-scale Experiment on Enrichment of Nitrifying Activated Sludge and Its Application in Enhancing a Wastewater Biological Treatment System Against Ammonia Shocking Loads]

Nitrifying activated sludge (NAS) was enriched in a membrane bioreactor (MBR) with pre-treated municipal wastewater and additional ammonium sulfate as the culture medium. The influences of temperature, dissolved oxygen (DO), ammonia nitrogen volumetric load, free ammonia (FA), and free nitrite (FNA) on the enrichment of NAS were investigated, the cost of the process was evaluated, and then NAS's application in enhancing a wastewater biological treatment system against ammonia shocking loads was attempted. The results showed that after 182 days of cultivation in an MBR, NAS had a nitrification activity of 98.41 mg·(L·h)^-1, which was 30-times higher than that of the seeding sludge. The yield of NAS was 14.96 mg·(L·d)^-1, costing 3.52 Yuan for 1 kg. Temperature was found to be a key factor affecting the sludge nitrification activity. The sludge nitrification activity was decreased to 1/3 of the maximum value at temperatures below 15.0℃, while lowering the ammonium volumetric load retarded the decrease in the sludge nitrification activity to some extent. In addition, dissolved oxygen deficiency resulted in nitrite accumulation, and thereby slowed down the NAS enrichment rate. The enriched NAS was then applied to a wastewater biological treatment pilot equipment, which had just been exposed to an ammonium shocking load. The removal rate of ammonia nitrogen in the biological system increased from 29.4% to 88.4% after 2.0% of NAS was inoculated. The enhanced biological system retained ammonia removal rates of as high as 99.0%, even as the temperature dropped to 13.3℃±1.6℃ afterwards. The above pilot-experiment results suggested that enriched nitrifying sludge is suitable for quickly increasing the start-up or recovery rates of the nitrifying function in a biological system.