The microbial processes involved in two-phase anaerobic digestion were investigated by operating a laboratory-scale acid-phase (AP) reactor and analyzing two full-scale, two-phase anaerobic digesters ...operated under mesophilic (35 °C) conditions. The digesters received a blend of primary sludge and waste activated sludge (WAS). Methane levels of 20% in the laboratory-scale reactor indicated the presence of methanogenic activity in the AP. A phylogenetic analysis of an archaeal 16S rRNA gene clone library of one of the full-scale AP digesters showed that 82% and 5% of the clones were affiliated with the orders Methanobacteriales and Methanosarcinales, respectively. These results indicate that substantial levels of aceticlastic methanogens (order Methanosarcinales) were not maintained at the low solids retention times and acidic conditions (pH 5.2-5.5) of the AP, and that methanogenesis was carried out by hydrogen-utilizing methanogens of the order Methanobacteriales. Approximately 43, 31, and 9% of the archaeal clones from the methanogenic phase (MP) digester were affiliated with the orders Methanosarcinales, Methanomicrobiales, and Methanobacteriales, respectively. A phylogenetic analysis of a bacterial 16S rRNA gene clone library suggested the presence of acetate-oxidizing bacteria (close relatives of Thermacetogenium phaeum, 'Syntrophaceticus schinkii,' and Clostridium ultunense). The high abundance of hydrogen consuming methanogens and the presence of known acetate-oxidizing bacteria suggest that acetate utilization by acetate oxidizing bacteria in syntrophic interaction with hydrogen-utilizing methanogens was an important pathway in the second-stage of the two-phase digestion, which was operated at high ammonium-N concentrations (1.0 and 1.4 g/L). A modified version of the IWA Anaerobic Digestion Model No. 1 (ADM1) with extensions for syntrophic acetate oxidation and weak-acid inhibition adequately described the dynamic profiles of volatile acid production/degradation and methane generation observed in the laboratory-scale AP reactor. The model was validated with historical data from the full-scale digesters.
A "fourth generation" down-flow hanging sponge (DHS) Reactor has been developed and proposed as an improved variant of post-treatment system for UASB treating domestic wastewater. This paper ...evaluates the potential of the proposed combination of UASB and DHS as a sewage treatment system, especially for developing countries. A pilot-scale UASB (1.15 m3) and DHS (0.38 m3; volume of sponge) was installed in a municipal sewage treatment site and constantly monitored for 2 years. UASB was operated at an HRT of 6 h corresponding to an organic load of 2.15 kg-COD/m3 per day. Subsequently, the organic load in DHS was 2.35 kg-COD/m3 per day, operated at an HRT of 2 h. Organic removal by the whole system was satisfactory, accomplishing 96% of unfiltered BOD removal and 91% of unfiltered COD removal. However, nitrification decreased from 56% during the startup period to 28% afterwards. Investigation on DHS sludge was made by quantifying it and evaluating oxygen uptake rates with various substrates. Average concentration of trapped biomass was 26 g-VSS/L of sponge volume, increasing the SRT of the system to 100-125 d. Removal of coliforms obtained was 3-4 log10 with the final count of 10(3) to 10(4) MPN/100 ml in DHS effluent.
This paper presents an evaluation of the process performance of a pilot-scale "fourth generation" downflow hanging sponge (DHS) post-treatment system combined with a UASB pretreatment unit treating ...municipal wastewater. After the successful operation of the second- and third-generation DHS reactors, the fourth-generation DHS reactor was developed to overcome a few shortcomings of its predecessors. This reactor was designed to further enhance the treatment efficiency and simplify the construction process in real scale, especially for the application in developing countries. Configuration of the reactor was modified to enhance the dissolution of air into the wastewater and to avert the possible clogging of the reactor especially during sudden washout from the UASB reactor. The whole system was operated at a total hydraulic retention time (HRT) of 8 h (UASB: 6 h and DHS: 2 h) for a period of over 600 days. The combined system was able to remove 96% of unfiltered BOD with only 9 mg/L remaining in the final effluent. Likewise, F. coli were removed by 3.45 log with the final count of 10(3) to 10(4) MPN/100 ml. Nutrient removal by the system was also satisfactory.
This study compares the performance of a pilot-scale combination of UASB and DHS system to that of activated sludge process (ASP) for the treatment of municipal sewage. Both systems were operated in ...parallel with the same sewage as influent. The study was conducted for more than 300 days, which revealed that organic removal efficiency of
UASB
+
DHS
system was comparable to that of ASP. Unfiltered BOD removal by both systems was more than 90%. However,
UASB
+
DHS
system outperformed ASP for pathogen removal. In addition, volume of excess sludge production from
UASB
+
DHS
was 15 times smaller than that from ASP. Moreover, unlike ASP, there is no requirement of aeration for the operation of
UASB
+
DHS
system, which makes it an economical treatment system. Considering the above observations, it was concluded that
UASB
+
DHS
system can be a cost-effective and viable option for the treatment of municipal sewage over ASP, especially for low-income countries.
Combining the processes of partial nitrification and anaerobic ammonium oxidation (ANAMMOX) is an attractive wastewater-treatment technology for nitrogen removal. In this study we investigated ...partial nitrification by implementing a closed down-flow hanging sponge (DHS) reactor operated at controlled oxygen concentrations. Basic concept of DHS process is similar to that of trickling filter, in which oxygen concentration can be easily manipulated by controlling airflow to the reactor. The closed reactor was fed with artificial wastewater containing NH
4Cl and operated with an HRT of 1.5
h at 30
°C. Oxygen inside the reactor was maintained below 3% (1.2
mg
DO·L
−1) (DO—dissolved oxygen) except during the startup periods. Five months of continuous operation showed that there was a strong relationship between oxygen concentration and nitrite production. The ratio of nitrite produced relative to ammonium oxidized increased by decreasing oxygen concentration. Partial nitrification was satisfactorily accomplished under oxygen limitation at around 0.5% in the gas phase (0.2
mg
DO
L
−1). The system showed a high ammonium-removal rate, at a maximum of 1.46
kg NH
4
+–N
m
−3
day
−1, even at limited oxygen concentration. We also found that oxygen concentration played an important role in the production of nitrous oxide, which increased with decreasing oxygen concentration.
This paper presents an evaluation of the process performance of a pilot-scale “fourth generation” downflow hanging sponge (DHS) post-treatment system combined with a UASB pretreatment unit treating ...municipal wastewater. After the successful operation of the second- and third-generation DHS reactors, the fourth-generation DHS reactor was developed to overcome a few shortcomings of its predecessors. This reactor was designed to further enhance the treatment efficiency and simplify the construction process in real scale, especially for the application in developing countries. Configuration of the reactor was modified to enhance the dissolution of air into the wastewater and to avert the possible clogging of the reactor especially during sudden washout from the UASB reactor. The whole system was operated at a total hydraulic retention time (HRT) of 8 h (UASB: 6 h and DHS: 2 h) for a period of over 600 days.The combined system was able to remove 96% of unfiltered BOD with only 9 mg/L remaining in the final effluent. Likewise, F. coli were removed by 3.45 log with the final count of 103 to 104 MPN/100 ml. Nutrient removal by the system was also satisfactory.
In this paper, we explore older adults’ experiences moving daily social activities online in a senior independent living community during the early stages (March 2020–June 2020) of the Covid-19 ...pandemic in the United States. We present findings of a semi-structured interview study with eight older adult residents where we discuss their needs and how they used technology to support and adapt during the phase of required physical distancing. Our findings suggest that participants felt well supported by their organization and community, and found information and communication technologies (ICTs) that were useful for supporting the transition. However, some participants felt that they did face challenges and the ability to adapt may have been influenced by technology access and residents’ prior established ties within the community. Based on our findings, we reflect on how we might better support older adults living in community settings in future crisis.
A novel municipal wastewater treatment system, consisting of a combination of an upflow anaerobic sludge blanket (UASB) and down-flow hanging sponge (DHS) posttreatment unit, was continuously ...evaluated for more than three years with raw sewage as an influent. The system was installed at a sewage treatment site and operated at
25±3°C
. This paper reports on the results of a long term monitoring of the system. The whole experimental period was divided into three distinct phases with different operating conditions. Organic pollutants were only partially removed in anaerobic UASB pretreatment unit. The remaining organics as well as nitrogenous compounds were almost completely removed by the DHS posttreatment unit. In all phases the system demonstrated removal efficiency consistently over 95% for unfiltered biochemical oxygen demand (BOD), 80% for unfiltered-chemical oxygen demand and 70% for suspended solids. The system produced an excellent effluent quality with only
4–9
mg∕L
of residual unfiltered BOD. Dissolved oxygen in the final effluent was
5–7
mg∕L
although no aeration was provided to DHS system. Moreover, excess sludge production from DHS was negligible thus eliminating secondary sludge that is troublesome to dispose off. The system also exhibited substantial stability against twofold hydraulic shock load and fourfold organic shock load. The results suggested that the proposed system may be a competitive solution for municipal sewage treatment under variable conditions.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Sleep disorders and fatigue are highly prevalent in chronic kidney disease (CKD) and end-stage kidney disease (ESKD) patients but there is limited evidence on the effect of kidney transplant (KTx) on ...these.
In a prospective cohort study of patients with advanced CKD (estimated glomerular filtration rate<30 mL/min/1.73 m
) or ESKD, polysomnography and patient-reported symptom assessments were conducted. Pre- and post-KTx changes in sleep apnea (SA) severity (measured by apnea hypopnea index AHI) were analyzed and compared with patients who did not receive KTx. Regression models were used to examine predictors of SA severity.
Among 77 patients (mean age 51 y, BMI 29 kg/m
, 66% males, 23% ESKD), 61% had SA at baseline. Among 39 KTx recipients, 56% had SA, with 39% having moderate-severe SA after 10 ± 5.6 months post-KTx. There was no difference in AHI in either the KTx (median 6 versus 8;
= 0.37) or no-KTx (median 15 versus 16;
= 0.61) groups after an average of 19.9 ± 8.9 months. KTx led to significant clinically meaningful improvements in fatigue and health-related quality of life (adjusted effect size 0.3-0.6). In multivariable regression, baseline AHI was the only significant predictor of SA severity (adjusted β = 3.6/5 units, 95% confidence interval 2.1, 5.2) after adjusting for KTx status, age, sex, and body mass index.
More than half of the KTx recipients had SA. There was no significant change in SA severity with KTx. Clinically meaningful moderate size improvements in patient-reported fatigue and health-related quality of life may be seen with KTx.
We previously reported that partial nitrification in the down-flow hanging sponge (DHS) system was satisfactorily accomplished under oxygen-limited conditions Chuang
et al., Water Res., 41, 295–302 ...(2007). In this study, we investigated the microbes that are responsible for the partial nitrification in this unique system by 16S rRNA- and
amoA-based cloning analyses and fluorescence
in situ hybridization. Microbes related to
Nitrosomonas species were found to be chiefly responsible for catalyzing the partial nitrification. Microbes affiliated with the uncultivated phyla OP10 and
Bacteroidetes were also numerous in the DHS, but their ecological niches are still unknown.
PDF
