Quantitative detection and reduction of potentially pathogenic bacterial groups of Aeromonas, Arcobacter, Klebsiella pneumoniae species complex, and Mycobacterium in wastewater treatment facilities.

Water quality parameters influence the abundance of pathogenic bacteria. The genera Aeromonas, Arcobacter, Klebsiella, and Mycobacterium are among the representative pathogenic bacteria identified in wastewater. However, information on the correlations between water quality and the abundance of these bacteria, as well as their reduction rate in existing wastewater treatment facilities (WTFs), is lacking. Hence, this study aimed to determine the abundance and reduction rates of these bacterial groups in WTFs. Sixty-eight samples (34 influent and 34 non-disinfected, treated, effluent samples) were collected from nine WTFs in Japan and Thailand. 16S rRNA gene amplicon sequencing analysis revealed the presence of Aeromonas, Arcobacter, and Mycobacterium in all influent wastewater and treated effluent samples. Quantitative real-time polymerase chain reaction (qPCR) was used to quantify the abundance of Aeromonas, Arcobacter, Klebsiella pneumoniae species complex (KpSC), and Mycobacterium. The geometric mean abundances of Aeromonas, Arcobacter, KpSC, and Mycobacterium in the influent wastewater were 1.2 × 104-2.4 × 105, 1.0 × 105-4.5 × 106, 3.6 × 102-4.3 × 104, and 6.9 × 103-5.5 × 104 cells mL-1, respectively, and their average log reduction values were 0.77-2.57, 1.00-3.06, 1.35-3.11, and -0.67-1.57, respectively. Spearman's rank correlation coefficients indicated significant positive or negative correlations between the abundances of the potentially pathogenic bacterial groups and Escherichia coli as well as water quality parameters, namely, chemical/biochemical oxygen demand, total nitrogen, nitrate-nitrogen, nitrite-nitrogen, ammonium-nitrogen, suspended solids, volatile suspended solids, and oxidation-reduction potential. This study provides valuable information on the development and appropriate management of WTFs to produce safe, hygienic water.

Detection of potentially pathogenic Arcobacter spp. in Bangkok canals and the Chao Phraya River.

The management of pathogenic bacteria in waterways is a public health issue. Here, we investigated the concentrations of potentially pathogenic bacteria, Arcobacter spp. and Campylobacter spp., and Escherichia coli, by quantifying species-specific genes in surface water samples from canals and the Chao Phraya River from June 2017 to June 2018 in Bangkok, Thailand. We assessed the relationship between the specific bacterial concentrations, water quality, and seasonal changes. Arcobacter spp. were detected at high density in all samples and showed seasonal fluctuations according to analyses based on 16S rDNA and the invasion gene ciaB. High levels of 16S rDNA and dut gene of E. coli were detected in the polluted drainage canals. A high correlation was observed between E. coli and chemical and biochemical oxygen demand (COD and BOD), suggesting that untreated domestic wastewater was the source of the E. coli. In contrast, Arcobacter spp. were detected with high density even in water samples with relatively low COD, suggesting that Arcobacter spp. are more likely than E. coli to survive in the water environment. The analysis of 16S rDNA and ciaB gene sequence analyses indicated that the Arcobacter spp. isolated from the drainage canals were A. butzleri and A. cryaerophilus.

Performance evaluation of a down-flow hanging sponge (DHS) reactor as a decentralized domestic wastewater treatment system in tropical regions.

In this study, a pilot-scale down-flow hanging sponge (DHS) reactor was operated in the community plant of Bangkok for the treatment of domestic wastewater (COD 285 mg/L, BOD 105 mg/L) collected by separate sewer to evaluate the reactor's feasibility as a decentralized treatment system. The DHS reactor was operated for 600 days at ambient temperatures of 25-30 °C, both with constant flow conditions and with fluctuating flow conditions that simulated wastewater discharge patterns of the community. The results indicate that under constant flow at an HRT of 5 h, the volumetric loading rates of 0.36 kgBOD/m3-sponge/day and 0.16 kgN/m3-sponge/day were the optimum operational conditions of the DHS reactor in order to satisfy the effluent discharge standards. The DHS achieved removal rates of 89, 95, 91 and 90% for COD, BOD, TSS and NH4-N. Under the fluctuating flow condition, improvement of denitrification was confirmed at volumetric loading rates of 0.50 kgBOD/m3-sponge/day and 0.18 kgN/m3-sponge/day. The fluctuating flow of wastewater positively affects retained sludge activities in terms of homogenizing sludge concentration and stimulating oxygen uptake rates. These results suggest that the DHS reactor can be applied as a decentralized treatment system for domestic wastewater with fluctuating flow rates in tropical regions.

Evaluation of the process performance of a down-flow hanging sponge reactor for direct treatment of domestic wastewater in Bangkok, Thailand.

This study assesses the performance of an aerobic trickling filter, down-flow hanging sponge (DHS) reactor, as a decentralized domestic wastewater treatment technology. Also, the characteristic eukaryotic community structure in DHS reactor was investigated. Long-term operation of a DHS reactor for direct treatment of domestic wastewater (COD = 150-170 mg/L and BOD = 60-90 mg/L) was performed under the average ambient temperature ranged from 28°C to 31°C in Bangkok, Thailand. Throughout the evaluation period of 550 days, the DHS reactor at a hydraulic retention time of 3 h showed better performance than the existing oxidation ditch process in the removal of organic carbon (COD removal rate = 80-83% and BOD removal rate = 91%), nitrogen compounds (total nitrogen removal rate = 45-51% and NH4+-N removal rate = 95-98%), and low excess sludge production (0.04 gTS/gCOD removed). The clone library based on the 18S ribosomal ribonucleic acid gene sequence revealed that phylogenetic diversity of 18S rRNA gene in the DHS reactor was higher than that of the present oxidation ditch process. Furthermore, the DHS reactor also demonstrated sufficient COD and NH4+-N removal efficiency under flow rate fluctuation conditions that simulates a small-scale treatment facility. The results show that a DHS reactor could be applied as a decentralized domestic wastewater treatment technology in tropical regions such as Bangkok, Thailand.

Protection of biomass from snail overgrazing in a trickling filter using sponge media as a biomass carrier: down-flow hanging sponge system.

This study investigated down-flow hanging sponge (DHS) technology as a promising trickling filter (TF) using sponge media as a biomass carrier with an emphasis on protection of the biomass against macrofauna overgrazing. A pilot-scale DHS reactor fed with low-strength municipal sewage was operated under ambient temperature conditions for 1 year at a sewage treatment plant in Bangkok, Thailand. The results showed that snails (macrofauna) were present on the surface of the sponge media, but could not enter into it, because the sponge media with smaller pores physically protected the biomass from the snails. As a result, the sponge media maintained a dense biomass, with an average value of 22.3 gVSS/L sponge (58.1 gTSS/L sponge) on day 370. The snails could graze biomass on the surface of the sponge media. The DHS reactor process performance was also successful. The DHS reactor requires neither chemical treatments nor specific operations such as flooding for snail control. Overall, the results of this study indicate that the DHS reactor is able to protect biomass from snail overgrazing.

Development of a down-flow hanging sponge reactor for the treatment of low strength sewage.

The process performance of a down-flow hanging sponge (DHS) reactor for treating low strength sewage (biochemical oxygen demand (BOD) 20-50 mg/L) was investigated in Bangkok, Thailand. The hydraulic retention time (HRT) was set at 4 h during the start-up period and was reduced to 1.5 h in a stepwise manner. Throughout the 300-day operational period, the DHS reactor shows high performance with respect to the removal of total suspended solid (>90% total suspended solid removal efficiency). No clogging of sponge media was observed in response to the self-digestion phenomena of the biofilm. At a HRT of 1.5 h, the BOD removal efficiency was sufficiently high (about 85%). The pathogen Escherichia coli and other coliform bacteria were removed almost completely as well (removal was 99.4% and 98.1%, respectively). Regarding the retained sludge activity measurement, the nitrite oxidation rate was higher than the ammonium oxidation rate (0.031 and 0.022 gram of nitrogen per gram of volatile suspended solids per day, respectively). In the 300 days of operation, the amount of excess sludge production was negligible. Thus, no sludge treatment system is required. Introduction of the DHS system in developing countries is recommended because this system requires a relatively small area, and has low electricity consumption and operation costs.

Pilot-scale experiment of down-flow hanging sponge for direct treatment of low-strength municipal wastewater in Bangkok, Thailand.

A pilot-scale experiment of a down-flow hanging sponge (DHS) reactor for treatment of low-strength municipal wastewater was conducted over 1 year in Bangkok, Thailand, to establish an appropriate method for treatment under tropical climate conditions. Municipal wastewater with an average BOD of 19 mg/L was fed directly into the DHS reactor. Superior effluent quality (5.1 ± 3.4 mg/L TSS, 21.1 ± 9.0 mg/L COD, 2.8 ± 1.4 mg/L BOD, and 4.1 ± 1.0 mg/L TN) was achieved at a hydraulic retention time (HRT) of 1 h under an average temperature of 30 °C. The DHS reactor reached an actual HRT of 19.0 min, indicating good contact efficiency between wastewater and retained sludge. The DHS reactor retained dense sludge at 15.3-26.4 g VSS/L based on the sponge media volume. The sludge activity in terms of specific oxygen uptake rate was good. Excess sludge was produced as 0.051 g TSS/g COD removed (0.11 g TSS/g BOD removed), and a good SVI of 28 mL/g was observed. The sufficient performance was attributed to dense sludge with high activity, regardless of the low-strength wastewater. Overall, the DHS was advantageous owing to its simple operation, lack of operational problems, and low power consumption.

Development of appropriate technology for treatment of molasses-based wastewater.

In this study, the performance of a proposed treatment system consisting of an anaerobic process (acidification, methane fermentation) and an aerobic process (trickling filter) was evaluated for treating high concentrations of molasses-based wastewater (43-120 gCOD/L) by a continuous flow experiment. An anaerobic up-flow staged sludge bed (USSB) reactor, equipped with multiple gas solid separators, was used as the main treatment/methane recovery process. The USSB showed good efficiency of both COD removal (80-87%) and methane recovery (70-80%) at an organic loading rate of 11-43 kgCOD/m(3) day. As the influent COD concentration was increased, the organic loading rate for stable operation of the USSB was reduced due to cation inhibition. However, the COD removal efficiency of the whole treatment system (including the aerobic post-treatment process) was 96% even at an influent COD concentration of 120 gCOD/L. Use of the treated wastewater as a fertilizer and/or irrigation-water for sugarcane was evaluated by a field cultivation test. Both growth of sugarcane and emission of greenhouse gases from the field soil were measured. A relatively high methane flux (352 µgCH4/m(2) h) was observed when the treated wastewater from day 0 was used. By day 3, however, this value was reduced to the same level as the control. In addition, growth of sugarcane was satisfactory when the treated wastewater was used. The treated wastewater was found to be useful for cultivation of sugarcane in terms of both a low risk of greenhouse gas emission from the field soil and effectiveness for growth of sugarcane.

Development of a treatment system for molasses wastewater: the effects of cation inhibition on the anaerobic degradation process.

This study evaluated the process performance of a novel treatment system consisting of an acidification reactor, an upflow staged sludge bed (USSB) reactor, an upflow anaerobic sludge blanket reactor, and an aerobic trickling filter for the treatment of a high-strength molasses wastewater with a chemical oxygen demand (COD) of up to 120,000mg/L. The USSB operating at 35°C was capable of achieving an organic loading rate of 11kgCOD/m(3) day with a methane recovery of 62.4% at an influent COD of 120,000mg/L. The final effluent COD was 4520mg/L. The system was effective with regard to nitrification and sulfur removal. Fifty percent inhibition of the bacterial activity of the retained sludge by the cations was determined at 8gK/L for sucrose degradation, 16gK/L for sulfate reduction, and 12gK/L or 9gNa/L for acetoclastic methane production. Cation inhibition of anaerobic degradation reduced the process performance of the USSB.

High-rate treatment of molasses wastewater by combination of an acidification reactor and a USSB reactor.

A combination of an acidification reactor and an up-flow staged sludge bed (USSB) reactor was applied for treatment of molasses wastewater containing a large amount of organic compounds and sulfate. The USSB reactor had three gas-solid separators (GSS) along the height of the reactor. The combined system was continuously operated at mesophilic temperature over 400 days. In the acidification reactor, acid formation and sulfate reduction were effectively carried out. The sugars contained in the influent wastewater were mostly acidified into acetate, propionate, and n-butyrate. In addition, 10-30% of influent sulfur was removed from the acidification reactor by means of sulfate reduction followed by stripping of hydrogen sulfide. The USSB achieved a high organic loading rate (OLR) of 30 kgCOD m(-3) day(-1) with 82% COD removal. Vigorous biogas production was observed at a rate of 15 Nm(3) biogas m(-3) reactor day(-1). The produced biogas, including hydrogen sulfide, was removed from the wastewater mostly via the GSS. The GSS provided a moderate superficial biogas flux and low sulfide concentration in the sludge bed, resulting in the prevention of sludge washout and sulfide inhibition of methanogens. By advantages of this feature, the USSB may have been responsible for achieving sufficient retention (approximately 60 gVSS L(-1)) of the granular sludge with high methanogenic activity (0.88 gCOD gVSS(-1) day(-1) for acetate and as high as 2.6 gCOD gVSS(-1) day(-1) for H(2)/CO(2)). Analysis of the microbial community revealed that sugar-degrading acid-forming bacteria proliferated in the sludge of the USSB as well as the acidification reactor at high OLR conditions.

Microbial community structure and population dynamics of granules developed in expanded granular sludge bed (EGSB) reactors for the anaerobic treatment of low-strength wastewater at low temperature.

The anaerobic biological treatment of sucrose-based, low-strength wastewater was investigated in expanded granular sludge bed (EGSB) reactors at low temperatures over a 300-day trial period. During the trial, the operating temperature was lowered in a stepwise manner from 20 degrees C to 5 degrees C. As a result, the reactors exhibited sufficient performances until 10 degrees C operation. The COD removal rate was 3.1-3.8 kgCOD m(-3) day(-1) at 10 degrees C. In particular, the COD removal rate increased gradually through the low-temperature operation; indeed, the later stages of the 10 degrees C operation attained a rate similar to those achieved at 20 degrees C and 15 degrees C. This finding is especially practical for applications of psychrophilic methane fermentation. Additionally, the structure of the microbial community in the granular sludge was analyzed by clone analysis based on 16S rRNA genes and fluorescence in situ hybridization (FISH). As a result, the percentage of the phylum Firmicutes, which were assumed to be Anaerobivrio sp. and Lactococcus sp., greatly increased from 0.7% to 8.0% of the total cells, especially in the surface layer of the granular sludge. These bacteria would contribute to the degradation of the sucrose substrate anaerobically at ambient temperatures. Moreover, the results suggest that a Methanospirillum species, which is a H2-utilizing methanogen, increased from 0.5% to 6.7% during the low-temperature incubation, with a significant increase of methanogenic activity from H2/CO2 at 20 degrees C. Thus, the Methanospirillum species detected in this study may have a key role as hydrogen scavenger during hydrogen-metabolism in low-temperature conditions.

Influence of sugar content of wastewater on the microbial characteristics of granular sludge developed at 20 degrees C in the anaerobic granular sludge bed reactor.

The influence of the sugar content of wastewater on changes in the characteristics of the retained sludge was investigated by using two lab-scale granular sludge bed reactors at 20 degrees C. Both reactors were inoculated with granular sludge grown at 20 degrees C and were fed with synthetic wastewater containing sucrose and volatile fatty acids (VFAs). On day 70, the sucrose content of the wastewater was changed to 90% (based on wastewater COD value) for the first reactor and 0% (VFA 90%) for the second. After this change in feed composition, the COD removal efficiency became about 91% for the sucrose-fed reactor and 95% for the VFA-fed reactor. The growth yield (Yg) of the sucrose-fed sludge increased more than that of the VFA-fed sludge. Consequently, deterioration of the settleability of the sucrose-fed sludge was observed. The sucrose-degrading activity of the retained sludge obtained from the sucrose-fed reactor increased significantly from 3.7 g COD g VSS(-1) day(-1) on day 62 to 36.8 g COD g VSS(-1) day(-1) on day 230, in accordance with the predominant growth of sugar-degrading bacteria--namely, Lactococcus, Clostridium and Chloroflexi--in the retained sludge. The excessive growth of these sugar-degrading bacteria in the retained sludge caused unstable process performance in the sucrose-fed reactor at 20 degrees C.

Changes in process performance and microbial characteristics of retained sludge during low-temperature operation of an EGSB reactor.

A lab-scale expanded granular sludge bed (EGSB) reactor was seeded with granular sludge and operated to investigate the influence of temperature decrease on both process performance and the microbial community structure of the granular sludge. Synthetic wastewater containing sucrose and volatile fatty acids was used as feed. The EGSB reactor was brought online at a starting temperature of 15 degrees C and was reduced stepwise to a final temperature of 5 degrees C. The reactor exhibited sufficient COD removal efficiency between 10 degrees C and 15 degrees C. However at 5 degrees C serious deterioration of process performance was observed. The methane-producing activity of the retained sludge increased when it was compared to the activity of the seed sludge (day 0) during 10 degrees C to 15 degrees C operation. When hydrogen fed, sludge showed much higher methanogenic activity as compared with seed sludge activity at test temperatures of 15 degrees C and 20 degrees C on day 196 of reactor operation. At this time, proliferation of the genus Methanospirillum in the retained sludge was observed and a decrease in Methanobacterium species was also measured. Throughout the experiment, the genus Methanosaeta was detected in abundance and the community structure of the Domain Bacteria was stably maintained. The sugar-degrading acid-forming bacteria, Lactococcus and Anaerovibrio were detected in the retained sludge throughout the experiment as well and the propionate-degrading acetogen Syntrophobacter fumaroxidans was also detected, although its population size decreased at 5 degrees C.