Clean rivers and healthy aquatic life symbolize that the ecosystem is functioning well. The Ganga River has shown signs of rejuvenation and a significant improvement on many parameters, following the ...eight-week nationwide lockdown due to coronavirus pandemic. Since industrial units and commercial establishments were closed, water was not being lifted by them with a negligible discharge of industrial wastewater. It was observed that during the lockdown period most of the districts falling under the Ganga basin observed 60% excess rainfall than the normal, which led to increased discharge in the river, further contributing towards the dilution of pollutants. Further, data analysis of live storages in the Ganga Basin revealed that the storage during the beginning of the third phase of lockdown was almost double than the storage during the same period the previous year. Analysis of the storage data of the last ten years revealed that the storage till May 6, 2020 was 82.83% more than the average of the previous ten years, which meant that more water was available for the river during the lockdown period. The impact could be seen in terms of increased dissolved oxygen (DO) and reduced biological oxygen demand (BOD), Faecal coliform, Total coliform and nitrate (NO3-) concentration. A declining trend in nitrate concentration was observed in most of the locations due to limited industrial activities and reduction in agricultural run-off due to harvesting season. The gradual transformation in the quality of the water has given a sign of optimism from the point of restoration. Yet, it is believed that this improvement in water quality is ‘short-lived’ and quality would deteriorate once the normal industrial activities are resumed, indicating a strong influence of untreated commercial–industrial wastewater. The paper concludes that the river can be rejuvenated if issues of wastewater and adequate flow releases are addressed.
Display omitted
•Signs of rejuvenation and significant improvement on many parameters in Ganga River, following nationwide lockdown due to coronavirus pandemic•Lockdown period coincides excess rainfall (60 percent above normal), reduced irrigation and power demands in the basin resulting in increased storages and more flow in the river improving the quality•Increasing trends of dissolved oxygen (DO) and decreasing trends of biological oxygen demand (BOD) and nitrate (NO3-) concentration•River becomes fit for drinking (Class A) in the upper stretches and for outdoor bathing (Class B) in the middle and lower stretches
•The NRE reached 77.8 ± 4.3% even COD/TIN ratio at 2.9 during 548 days of study.•The effect of PD/A will be enhanced after the added anammox biocarriers adapted.•Anammox bacteria abundance on ...biocarriers remained stable and was higher than WWTPs.•PD/A contributed about 32–47% nitrogen loss in hypoxic zones in step-feed AAO reactor.
The application of partial denitrification coupling with anammox (PD/A) in municipal sewage treatment is one of the most promising research field, and it has just begun. In 548 days of experiment treating real domestic sewage, the continuous flow reactor was started up by adding biocarriers containing anammox bacteria and operated stably after acclimatization. The PD/A was successfully achieved in the step-feed AO system. Furthermore, mass balance of ammonium revealed that anammox could contribute 32–47% to nitrogen loss. Compared with no biocarriers addition phase, the nitrogen removal efficiency (NRE) increased to 77.8 ± 4.3% and the effluent total inorganic nitrogen (TIN) decreased to 11.0 ± 2.1 mg/L at the COD/TIN ratio of 2.9 from day 428 to day 548 under the condition of anammox biocarriers addition and without external carbon source. Quantitative polymerase chain reaction (qPCR) and high-throughput sequencing analysis showed that anammox bacteria on the biological carrier accounted for 3.06% of the total bacteria in the stable phase, which was much higher than the reported <0.003% in wastewater treatment plants (WWTPs). After 247 days of operation with anammox biocarriers addition, the abundance of anammox bacteria on the carriers tended to be stable at 3.36 × 1010 gene copies g−1 dry sludge. The activity of anammox decreased and maintained at 13.14 g NH4+-N m−3 d−1 under the biocarriers-only condition, while increased from 11.71 g NH4+-N m−3 d−1 to 25.65 g NH4+-N m−3 d−1 in the hybrid condition of biocarriers and flocs. This study indicated that PD/A is effective to strengthen nitrogen removal with low COD/TIN ratio.
Display omitted
•Alkali-acid modified MS-biochar was superior to single alkali/acid modified ones in adsorption performance.•SNMS-800 owing obviously increased porosity showed enhanced TC adsorption ...reaching to 286.913 mg/g.•Magnetic sludge biochar’s pore size was closely related to its TC adsorption strength.•Pyrolysis temperatures showed great influence on MS-biochars’ property.•SNMS-800 showed stable TC adsorption in natural water samples along with good reusability.
Municipal sewage sludge (MS)-derived biochar shows low-cost superiority as a potential adsorbent in organic contaminants removal, but limited by its poor adsorption capacity and heavy metal leaking risk. Herein, a novel and effective alkali-acid combined method was proposed for its modification and applied to tetracycline adsorption. The associative facilitation between the alkali and acid modifications was explored, and the influences of pyrolysis temperatures on MS-biochar’s properties were investigated. The successfully preserved γ-Fe2O3 vested SNMS-800 with magnetism. It turned out that SNMS-800 exhibited optimum performance for tetracycline removal with adsorption capacity up to 286.913 mg/g, where all goodness-of-fit indexes of isothermal models were measured by MPSD model. The strong adsorption mechanisms were dominated by two considerable interactions, including strong π-π stacking interaction and pore-filling effect due to the significantly enhanced porosity which was proved by density functional theory model calculations. It manifested that appropriate multiple relation (1.7–6 times) between adsorbent’s pore size and adsorbate size closely related to the adsorption strength. The remarkably improved and stable adsorption capacity, extremely low-cost, easy magnetic preparation, and good reusability in natural water samples entrusted SNMS-800 with good potential for actual aqueous contaminant removal on a large scale. Meanwhile, it provides a clue for materials modification starting with its specific components, and supplies a cost-effective way for municipal sewage sludge’s resource disposal.
Elimination of nitrogen pollution from wastewater containing high-strength nitrate (NO3−-N) is a significant issue to prevent deterioration of water quality and eutrophication of receiving water ...body. Traditional denitrification process faces several challenges including the huge organic carbon demand, intermediate products accumulation, and long acclimatization period. In this study, an efficient solution was given by a novel two-stage Partial Denitrification (PD)-Anammox process. High NO3−-N (1000 mg N/L) wastewater and municipal sewage (COD: 182.5 mg/L, ammonia (NH4+-N): 58.3 mg/L) were simultaneously introduced to the PD reactor for NO3−-N converting to NO2−-N. The NH4+-N and NO2−-N in effluent of PD were removed in subsequent anammox reactor. Results showed that a satisfactory nitrogen removal was achieved by optimizing the volume ratios of influent NO3−-N and municipal sewage, as well as the external organic matter dosage. The NO3−-N removal efficiency reached up to 95.8% without accommodation period, along with the NH4+-N removal achieving 92.8%. Anammox contributed to 78.9% of TN removal despite the high COD (76.5–98.6 mg/L) in PD effluent was introduced, indicating the significant stability of the integrated process. The microbial analysis suggested that the Candidatus Brocadia, identified as anammox bacteria, cooperated stable with denitrifying bacteria in 215-day operation. The PD-Anammox process offers an economically and technically attractive approach in the high NO3−-N wastewater treatment since it has great advantages of much low carbon demand, minimal sludge production, enabling simultaneous treatment of municipal sewage, and avoiding the common issues in traditional denitrification process.
Display omitted
•Simultaneous treatment of high-strength nitrate and municipal sewage was demonstrated.•Nitrate removal efficiency reached up to 95.8% at influent nitrate of 1000 mg/L.•Municipal sewage was treated with nitrogen removal efficiency of 92.8%.•Anammox and denitrifying bacteria cooperated for advanced nitrogen removal.•Partial-denitrification combining with anammox is an economic and efficient option.
•Organic species and concentrations are critical factors for anammox-based process.•PN/A-based process with different operational strategies needed further exploration.•Effect of residual organics ...from A-stage is need concerned applying of sewage PN/A.•PN/A-based process combined with denitrification may be an effective process.•Influent organics could be an essential factor for successful application of sewage PN/A.
Partial nitrification-anammox (PN/A) is an energy-efficient process for nitrogen removal from sewage. The influent organics of sewage is usually pre-removed, reducing the risk for enriching anammox bacteria (AnAOB). However, recent studies demonstrate that optimum influent organics could improve nitrogen removal and operational stability of PN/A. Thus, the impact of organics on PN/A-based process should not be overlooked. In this review, the complicated impacts of organics-containing influent on anammox and their linking to apply PN/A are discussed. Firstly, the effect of organics on AnAOB metabolism and the competition relationship between AnAOB and heterotrophic bacteria are summarized. Secondly, the combined effects of influent organics and operational strategies on PN/A-based process were reviewed. Thirdly, how to control influent organics in the real application of PN/A were discussed. Lastly, recent development of the PN/A-based process combined with denitrification were reviewed. Overall, influent organics could be an essential factor for successful application of sewage PN/A.
Municipal sewage sludge is a significant by-product in the conventional treatment of municipal wastewater. Its output has greatly increased with the progress of urbanization and industrialization. ...The harmless disposal and resource utilization of municipal sewage sludge has become an urgent problem to be solved in the environment field. Incineration is a relatively mature technology for harmless disposal of municipal sewage sludge but faces pollutant emission and high cost problems. In this work, the latest research progress on municipal sewage sludge incineration and its pollutant control is summarized and analyzed systematically. Sludge co-combustion in municipal solid waste incinerators, coal-fired power plants and cement kilns does not require new sludge incineration equipments and flue gas treatment equipments. At the same time, co-combustion is also more environmentally friendly under certain circumstances. Staged air combustion, low oxygen dilution combustion and other methods can optimize combustion and effectively control nitrogen oxide emission during sludge combustion. Ca-based additives have significant effect on sulfur removal. Cl-containing compounds affect the volatilization of heavy metals and the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans.
Display omitted
•Optimizing the combustion process is a source control method to reduce NOx.•Ca-containing additives are excellent in the retention of the S element.•Chlorine can effectively promote the volatilization of some heavy metals.•N-containing compounds inhibit the formation of PCDD/Fs during sludge combustion.
Treatments for and methods of disposing of municipal sewage sludge have a limited ability to produce high-value products. The number of studies on using sludge for energy recovery—including those ...that use sludge lipids to produce biodiesel—has increased considerably. This study reviews and compares methods for all steps in the process of producing biodiesel from municipal wastewater sludge, including sludge pretreatment and lipid extraction methods, catalyst selection, and byproduct generation, and its economics analysis. Sludge drying by heat maybe the most efficient method but cost a lot, and drying by vacuum and chemicals are expected for future advancement. In the lipid extraction, organic solvents are costly and unfavorable to the environment. Therefore, alternative extractant that are more efficient, and environmentally friendly are of potential use but still need price reduction. In terms of catalysts, H2SO4 is an efficient and cheap catalyst in practical use but consumes a lot in operation. Solid acid catalysts are promising alternatives because of cost saving and environmental benign. Some new catalysts such as ionic liquid and enzymes are just promising in the much further future. The byproducts of different biodiesel production processes have been classified and been made downstream and environmental risk analysis. The optimization and greenness of catalysts and byproducts promote the commercialization of sewage sludge for biodiesel production. In addition, biodiesel refining by membrane technique is promising.
Display omitted
•Sludge biodiesel production processes are reviewed and compared.•Solid acid catalysts are promising alternatives for H2SO4.•Byproducts classified, downstream oriented and environmental risk analyzed.
•A continuous self-circulating up-flow granular sludge bed process was introduced.•Accurate self-circulating multiple times and O2 supply were driven only by aeration.•High up-flow velocity of 7–16 ...m/h contributed to particle formation and stability.•HRT of 10 h and DO of 0–0.3 mg/L were optimized for higher OLR and energy savings.•Self-circulation driven by aeration is key factor regulating nitrogen removal.
Aerobic granular sludge (AGS) capable of nitrogen and phosphorus removal is mainly limited to the applications in sequencing batch reactors. This study introduced an innovative continuous self-circulating up-flow fluidized bed process (Zier process) using separate aeration. The process was composed of an anoxic column (Zier-A), aeration column (Zier-OO) and aerobic column (Zier-O), and was used to treat actual municipal sewage continuously for 170 days. The process achieved self-circulation of 20–32 times and an up-flow velocity within the reactor of 7–16 m/h which were accurately controlled with only separate aeration. The larger proportion of self-circulating multiple times contributed to particle formation and stability, providing hydraulic shear conditions, and screened the precipitation performance of the granular sludge (GS). Meanwhile, the dissolved oxygen (DO) of Zier-O was controlled at 0.1–0.3 mg/L, and the DO of Zier-A input water was zero. The accurate oxygen supply enhanced simultaneous nitrification and denitrification (SND) as well as short-cut nitrification and denitrification in Zier-O and improved the COD utilization rate and the nitrogen removal rate in Zier-A. The COD treatment capacity reached 2.46 kg-COD/(m³·d). With a hydraulic retention time of 10 h, the process consistently ensured that the average concentrations of ammonia nitrogen and total nitrogen in the effluent were maintained below 5 and 15 mg/L, respectively. Moreover, the process maintained the shape and stability of GS, the median diameter of GS ranged between 300–1210 μm, the percentage of mass with particle size distribution < 200 μm at a height of 150 cm within Zier-A and Zier-O accounted for as low as 0.04%–0.05%, and showed good settling performance. The suspended solids in effluent can be maintained at 50–80 mg/L. Overall, the unique structural setting and control method of the Zier process provide another approach for the application of continuous AGS treatment for municipal sewage.
Display omitted
Display omitted
•Sustainable bricks can be manufactured using MSS, BFS and kaolin.•The use of BFS as a flux improved the physicochemical properties of bricks.•Elevated temperature and BFS dose both ...enhanced the vitrification and densification mechanisms.•The fired bricks had excellent compressive strength, with a maximum value of up to 70 MPa.•Providing an effective method to valorize MSS and BFS wastes.
In recent years, the contradiction between the huge production of municipal sludge and industrial residue and the shortage of landfill space has driven the exploration of novel effective methods to valorize these solid wastes. In this research, blast furnace slag (BFS), municipal sewage sludge (MSS) and kaolin are combined innovatively as precursor materials to manufacture self-foaming porous bricks, and the sintering behavior of bricks under different BFS doses and sintering temperatures is deeply studied to reveal the development mechanism. The results indicate that the formation of Fe2O3-hematite during sintering leads to a reddish-brown appearance of the bricks, while the generation of CaAl2Si2O8-anorthite with lower melting points helps to enhance the vitrification process. Besides, the increase in BFS dose or sintering temperature has significant impacts on the evolution of the brick physicochemical properties. This occurs because changing the dose of BFS or sintering temperature can obviously regulate the internal morphological characteristics of bricks, such as particle consolidation, pore size and structural compactness. Among them, large-sized pores are considered as the weak areas of mechanical strength, which is also the responsibility for the worst compressive strength of bricks sintered at 1300 °C. Finally, under the optimal sintering conditions of 15 % BFS dose and 1250 °C sintering temperature, the compressive strength, water absorption, apparent porosity, bulk density and linear shrinkage of the resulting brick are 65 MPa, 0.45 %, 2.50 %, 2.34 g/cm3 and 19.56 %, respectively. Overall results demonstrate that using recycled sludge and waste slag in brick manufacturing can produce products with desired performance, providing preferable solutions for solid waste valorization and sustainable brick production.
Display omitted
•Textile dyeing sludge pyrolysis showed higher char yield and lower condensate yield.•Alkali and alkaline earth metals promoted sludge pyrolysis and CaO can retain sulfur.•Catalytic ...pyrolysis led to lower iodine and higher MB adsorption values for chars.•Higher MB adsorption values were obtained by municipal sewage sludge chars.•Heavy metals risk of MC were lower than TC, both MC and TC showed slight risks.
A comparative research was performed to evaluate the products yields and chars properties for pyrolysis of textile dyeing sludge (TDS) and municipal sewage sludge (MSS). The high fixed carbon (19.36 wt%) and low volatile (23.66 wt%) contents of TDS resulted in higher char yields and lower condensate yields. TDS char (TC) had a higher sulfur (S) retention efficiency than MSS char (MC) and CaO exhibited a great S retention effect in MC. More alkali and alkaline earth metals (e.g. Na, K, Mg and Ca) in MSS contributed to enhanced catalytic pyrolysis. In comparison to non-catalytic pyrolysis, chars from catalytic pyrolysis had lower iodine number and higher methylene blue (MB) adsorption value. MB adsorption values of MC (212.28–414.20 mg/g) were much higher than those of TC (84.32–156.07 mg/g). In contrast, heavy metals risk degrees of MC (4.20–7.56) were lower than those of TC (7.55–12.87), and heavy metals in TC and MC showed slight risks to environment.
PDF
