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The down-flow hanging sponge (DHS) process has been rigorously studied as a significant post-treatment of anaerobically pretreated sewage and later for broader applications in industrial wastewater and pre-settled sewage treatment. The DHS has several advantages over conventional wastewater treatment technologies, i.e., simple process control, less workforce requirement, less footprint, low construction, operation, and maintenance costs due to simple design and less mechanical parts. DHS technology requires no external aeration, which saves energy use and minimizes the associated costs. Low excess sludge yield in the DHS process adds to economic efficiency. DHS achieved high organics removal efficiency up to 99% with considerable nutrient and pathogen removals at extremely short HRT. Up-to-date, six DHS configurations have been developed and extensively tested at pilot scale applications under different operational conditions, i.e., HRTs, OLRs, and SRTs. Accordingly, the DHS module has successfully been translated into full-scale demonstration plants in Japan, India, Egypt, and Thailand. This paper comprehensively reviews the mechanism and development history of the DHS system. The process performance for municipal and industrial wastewaters treatment covers a broad range of parameters, i.e., organics, nutrients, pathogens (bacteria, viruses, parasites) has been summarized. The unique feature of sludge reduction efficiency of DHS is comprehensively discussed. Moreover, the process microbiology, energy efficiency, emerging application of DHS for direct sewage treatment, pilot and full-scale experiences in the last 20 years are also reviewed. DHS technology has not yet being fully explored, mainly for nutrients removal, process modelling, optimization of wastewater and air flow configurations in DHS reactor, and biomass growth, which could help for further advancement in the process for better performance and wider applications.

Needless to specify, controlling nitrogen and phosphorus discharge from wastewater treatment plants is synonymous with the prevention of eutrophication of surface waters, as one of the major issues related to water security. The present study investigates the performance of a pre-anoxic sequencing batch reactor (SBR) working on the basis of intermittent aeration, operated at varied carbon (bCOD) to nitrogen (C/N) ratio of 3, 7.5, and 10, and readily biodegradable (rbCOD) to slowly biodegradable (sbCOD) ratio of 0.1, 0.25, and 0.5. The findings revealed that an enhanced nitrogen removal was observed, together with higher C/N and rbCOD to sbCOD ratios. The results also show a consistent increase in total phosphorus removal with an increase in nitrogen removal. The phosphorus uptake of sludge varied from 0.02 – 0.045 mgP/mgVSS (avg. 0.031 ± 0.004), which resulted in enrichment levels of 0.88 – 1.68 times the stoichiometric value of 0.0267 mgP/mgVSS (avg. 1.45 ± 0.14). On an average basis, the assimilative total phosphate (TP) content was increased by 0.008 gTP/gNO -/3 -N removal rate. The excess phosphorus removal was due to the formation of poorly soluble polyvalent phosphate compounds, which was found based on dry analysis, which persisted as bound phosphate in the sludge.

Conventional sewage treatment techniques have shown low removal efficiency for emerging contaminants (ECs). Hence, more efficient treatment systems need to be investigated. The current stu...

A wide range of emerging contaminants such as pharmaceuticals, personal care products, flame retardants, synthetic hormones and food additives etc., which were used by society in recent past for various purposes but recently were quantified are becoming a concern for human and animal health care. These compounds are transported in various levels of food chain. In last few decades, emerging contaminants are getting more attention due to their potential impact on human, aquatic and animal health. An essential strategy of wastewater treatment is sewage sludge treatment and application of sludge as manure to enhance soil nutrient levels. However, the incomplete removal of emerging contaminants in wastewater and sorbed portion of contaminants got into the sludge that is applied to soil. There is high probability that these compounds will leach into the groundwater resulting in its pollution.

The characteristics of sludge retained in a down-flow hanging sponge reactor were investigated to provide a better understanding of the sewage treatment process in the reactor. The organic removal and sulfur oxidation conditions were found to differ between the first layer and the following three layers. It was found that 63% and 59% of the organic matter was removed in the first layer, even though the hydraulic retention time was only 0.2 h. It is thought that the organic removal resulted from aerobic and anaerobic biodegradation on the sponge medium. The sulfate concentration increased 1.5–1.9-fold in the first layer, with almost no subsequent change in the second to fourth layers. It was shown that oxidation of sulfide in the influent was completed in the first layer. The result of the oxygen uptake rate test with an ammonium nitrogen substrate suggested that the ammonium oxidation rate was affected by the condition of dissolved oxygen (DO) or oxidation–reduction potential (ORP).

Moving bed biofilm reactor based sewage treatment plants (STPs) have been installed in northern India over the last decade. As such, there are no performance evaluation studies of this technology in the region. Evaluation of four such STPs was carried out in terms of removal efficiencies of physico-chemical parameters, microbiological parameters and heavy metals. Results showed that the average chemical oxygen demand, biological oxygen demand, total suspended solids, total nitrogen and total phosphorus removal of all STPs ranged from 74 to 91%, 81 to 95%, 79 to 93%, 44 to 80% and 58 to 85%, respectively. Total and thermotolerant (faecal) coliform in the influent and effluent of STPs ranged from 1.5 × 104 to 9.3 × 107 most probable number (MPN)/100 mL and 0 MPN/mL to 2,400 MPN/mL, respectively. Heavy metal concentration (nickel, zinc, cadmium, iron, lead, chromium, and copper) in effluent samples of all the STPs was below Indian discharge limits except lead. Integrated efficiency (IE) of the STPs was also evaluated and the results showed that the actual IE of all STPs was 0–10% larger than standard IE, indicating the suitability of the technology in the region.

The anaerobic process for the treatment of municipal and industrial wastewater has been in practice for over a century. Apart from treatment of wastewater, the process has the advantage of lower sludge and biogas production that can save energy. Application of this process in a primary clarifier in such a way that there is simultaneous digestion of primary settled sludge and organic removal from wastewater can be more advantageous in an aerobic treatment plant. The paper discusses the performance of such a primary claridigester at ambient temperature. With a single hydraulic retention time (HRT) of 4.5 h, the organic (chemical oxygen demand (COD) and biochemical oxygen demand (BOD)) removal efficiency was 36.3% and 34.6%, respectively. The biosolid production rate was 0.383 g VSS/g COD removed or 0.818 g VSS/g BOD3 removed. However, biogas contains 80.8% methane and the COD mass balance revealed the loss of removed COD as 41.5% in the form of dissolved effluent from the claridigester. On account of sludge characterization, it was observed that nitrogen and zinc were present in highest concentration (2.55% and 1,776 mg/kg dry solids) and other nutrient and heavy metal parameters were within limits of not posing any risk of soil toxicity if disposed of for enrichment of soil.

The characteristics of the microbial community in a practical-scale down-flow hanging sponge (DHS) reactor, high in organic matter and sulfate ion concentration, and the seasonal variation of the microbial community composition were investigated. Microorganisms related to sulfur oxidation and reduction (2–27%), as well as Leucobacter (7.50%), were abundant in the reactor. Anaerobic bacteria (27–38% in the first layer) were also in abundance and were found to contribute to the removal of organic matter from the sewage in the reactor. By comparing the Simpson index, the abundance-based coverage estimator (ACE) index, and the species composition of the microbial community across seasons (summer/dry, summer/rainy, autumn/dry, and winter/dry), the microbial community was found to change in composition only during the winter season. In addition to the estimation of seasonal variation, the difference in the microbial community composition along the axes of the DHS reactor was investigated for the first time. Although the abundance of each bacterial species differed along both axes of the reactor, the change of the community composition in the reactor was found to be greater along the vertical axis than the horizontal axis of the DHS reactor.

Bacterial diversity of full scale rotary drum composter from biodegradable organic waste samples were analyzed through two different approaches, i.e., Culture dependent and independent techniques. Culture-dependent enumerations for indigenous population of bacterial isolates mainly total heterotrophic bacteria (Bacillus species, Pseudomonas species and Enterobacter species), Fecal Coliforms, Fecal Streptococci, Escherichia coli, Salmonella species and Shigella species showed reduction during the composting period. On the other hand, Culture-independent method using PCR amplification of specific 16S rRNA sequences identified the presence of Acinetobacter species, Actinobacteria species, Bacillus species, Clostridium species, Hydrogenophaga species, Butyrivibrio species, Pedobacter species, Empedobactor species and Flavobacterium species by sequences clustering in the phylogenetic tree. Furthermore, correlating physico-chemical analysis of samples with bacterial diversity revealed the bacterial communities have undergone changes, possibly linked to the variations in temperature and availability of new metabolic substrates while decomposing organics at different stages of composting.

Profile analysis of the down-flow hanging sponge (DHS) reactor was conducted under various temperature and organic load conditions to understand the organic removal and nitrification process for sewage treatment. Under high organic load conditions (3.21–7.89 kg-COD m−3 day−1), dissolved oxygen (DO) on the upper layer of the reactor was affected by organic matter concentration and water temperature, and sometimes reaches around zero. Almost half of the CODCr was removed by the first layer, which could be attributed to the adsorption of organic matter on sponge media. After the first layer, organic removal proceeded along the first-order reaction equation from the second to the fourth layers. The ammoniacal nitrogen removal ratio decreased under high organic matter concentration (above 100 mg L−1) and low DO (less than 1 mg L−1) condition. Ammoniacal nitrogen removal proceeded via a zero-order reaction equation along the reactor height. In addition, the profile results of DO, CODCr, and NH3-N were different in the horizontal direction. Thus, it is thought the concentration of these items and microbial activities were not in a uniform state even in the same sponge layer of the DHS reactor.

In this study, the effectiveness of polyvinyl alcohol (PVA) gel beads in treating domestic wastewater was investigated: a moving bed biofilm reactor (MBBR) configuration (oxic-anoxic and oxic) with 10% filling fraction of biomass carriers was operated in a continuously fed regime at temperatures of 25, 20, 15 and 6 °C with hydraulic retention times (HRTs) of 32 h, 18 h, 12 h and 9 h, respectively. Influent loadings were in the range of 0.22-1.22 kg N m(-3) d(-1) (total nitrogen (TN)), 1.48-7.82 kg chemical oxygen demand (COD) m(-3) d(-1) (organic) and 0.12-0.89 kg NH4(+)-N m(-3)d(-1) (ammonia nitrogen). MBBR performance resulted in the maximum TN removal rate of 1.22 kg N m(-3) d(-1) when the temperature and HRT were 6 °C and 9 h, respectively. The carbon removal rate at this temperature and HRT was 6.82 kg COD m(-3) d(-1). Ammonium removal rates ranged from 0.13 to 0.75 kg NH4(+)-N m(-3) d(-1) during the study. Total phosphorus and suspended solid removal efficiency ranged from 84 to 98% and 85 to 94% at an influent concentration of 3.3-7.1 mg/L and 74-356 mg/L, respectively. The sludge wasted from the MBBR exhibited light weight features characterized by sludge volume index value of 185 mL/g. Experimental data obtained can be useful in further developing the concept of PVA gel based wastewater treatment systems.

High rate composting studies of hard to degrade herbal wastes were conducted in a 3.5 m3 capacity rotary drum composter. Studies were spread out in four trials: In trial 1 and 2, one and two turns per day rotation was observed, respectively, by mixing of herbal industry waste with cattle (buffalo) manure at a ratio of 3:1 on wet weight basis. In trial 3 inocula was added in raw waste to enhance the degradation and in trial 4 composting of a mixture of vegetable market waste and herbal waste was conducted at one turn per day. Results demonstrated that the operation of the rotary drum at one turn a day (trial 1) could provide the most conducive composting conditions and co-composting (trial 4) gave better quality compost in terms of temperature, moisture, nitrogen, and Solvita maturity index. In addition a FT-IR study also revealed that trial 1 and trial 4 gave quality compost in terms of stability and maturity due to the presence of more intense peaks in the aromatic region and less intense peaks were found in the aliphatic region compared with trial 2 and trial 3.

Information on maturation process of primary stabilized compost from rotary drum composter for the mixed organic wastes is rather limited. Thus, seven different maturation methods namely windrow (L/W = 6, T1), windrow (L/W = 2.5, T2), vermicomposting (Eisenia foetida) (T3), packing in jute bags (T4), pile with longitudinal pipe for aeration (L/W = 6) (T5), pile with longitudinal pipe for aeration (L/W = 2.5, T6) and pile with lateral pipe for aeration (L/W = 6, T7) have been tried to optimize the maturation period. In addition, seasonal variation (ambient temperature and relative humidity) effects on maturation were also taken into account. The quality of matured compost was assessed by analyzing moisture content, pH, organic matter and stability parameters such as CO2 evolution rate and oxygen uptake rate (OUR). By examining these parameters, it is suggested that methods T3 (vermicomposting) and T1 (windrow, L/W = 6) were found suitable in delivering better quality matured compost within 20 days. A new relationship has been worked out between easily measurable parameters such as moisture content, pH, organic matter and the principal maturation parameter i.e., CO2 evolution rate and found to be satisfactorily applicable to check compost stability and maturity.

Removal efficiencies, kinetics and degradation pathways of aldrin, endosulfan α and endosulfan β in vegetable waste were evaluated during rotary drum and conventional windrow composting. The highest percentage removal of aldrin, endosulfan α and endosulfan β in rotary drum composting was 86.8, 83.3 and 85.3% respectively, whereas in windrow composting, it was 66.6%, 77.7% and 67.2% respectively. The rate constant of degradation of aldrin, endosulfan α and endosulfan β during rotary drum composting ranged from 0.410-0.778, 0.057-0.076 and 0.009-0.061 day(-1) respectively. The pathways of degradation of these pesticides in composting process were proposed. Metabolites dieldrin and 1 hydroxychlorodene formed during composting of aldrin in the vegetable waste indicated the occurrence of epoxidation reaction and oxidation of bridge carbon of aldrin containing the methylene group. Formation of chloroendic acid and chloroendic anhydride during composting of endosulfan containing vegetable waste support the occurrence of endosulfan sulfate and dehydration reaction respectively.

Hydrogen sulfide (H2S) is one of the main odorant gases emitted from anaerobic sludge blanket (UASB) sewage treatment plants (STPs) and other anaerobic environments. The present work is an attempt to quantify H2S formation in seven full-scale UASB reactors across India and suppression of sulfide formation using pilot-scale UASB reactors and adopting a liquid-phase odor and corrosion control method that enhances sulfate (SO42−) concentration in raw sewage up to 100–120 mg/L. Results for full-scale UASBs reveal that H2S varies 0–20.3 ppm because of high influent sulfates that range 100–150 mg/L as the result of ingress of industrial wastewater in domestic sewage. However, results for the pilot-scale UASBs reveal that SO42− in the influent (38–40 mg/L) converted to sulfide (15–20 mg/L) at ORP and pH to the safe range (ORP=−75 mV; pH=6.9–7.3). After sulfate enhancement, sulfide was observed to be 30–40 mg/L; COD removal, 80–85%; and ORP ranging from −65 to −103 mV. Furthermore, iron salt (FeCl3...

Fourier transform-infrared (FT-IR), Thermogravimetry (TG), Differential thermal analyses (DTA) and Differential Thermogravimetric (DTG) studies of a mixture of vegetable waste, saw dust, tree leaves and cow dung for microbial activity (feedstock) and their compost were reported in three different seasons i.e. winter, spring and summer. The correlation between spectral studies and compost composition provide information regarding their stability and maturity during composting. FT-IR spectra were conferred the functional groups and their intensity and TG, DTG and DTA for wt. loss, rate of wt. loss and enthalpy change in compost. Weight loss in feedstock and compost at two different temperatures 250–350 and 350–500°C was found 38.06, 28.15% for inlet and 14.08, 25.67% for outlet zones in summer and 50.59, 29.76% for inlet and 18.08, 25.67% in outlet zones in spring season, higher (5–10%) than winter. The corresponding temperatures in DTA in the samples from inlet to outlet zone were; endotherm (100–200°C), due to dehydration, exotherm (300–320°C), due to peptidic structure loss and exotherm (449–474°C) due to the loss of polynuclear aromatic structures, which were higher by 4°C and 10–20°C and rate of wt. loss was higher by 5–10% in spring and summer season, respectively than winter season composting, reported regardless of the maturation age of the compost. Relative intensity of exotherms (300–320/449–474°C) gave the thermally more stable fractions of organic compound. Our results indicated that the rotary drum composting of organic matters in spring and summer season gave higher molecular complexity and stability than the winter season.

High rate composting studies on institutional waste, i.e. vegetable wastes, tree leaves, etc., were conducted on a demonstration-scale (3.5 m 3 ) rotary drum composter by evaluating changes in some physico-chemical and biological parameters. During composting, higher temperature (60–70 °C) at inlet zone and (50–60 °C) at middle zone were achieved which resulted in high degradation in the drum. As a result, all parameters including TOC, C / N ratio, CO 2 evolution and coliforms were decreased significantly within few days of composting. Within a week period, quality compost with total nitrogen (2.6%) and final total phosphorus (6 g/kg) was achieved; but relatively higher final values of fecal coliforms and CO 2 evolution, suggested further maturation. Thus, two conventional composting methods namely windrow (M1) and vermicomposting (M2) tried for maturation of primary stabilized compost. By examining these methods, it was suggested that M2 was found suitable in delivering fine grained, better quality matured compost within 20 days of maturation period.