Laboratory-scale experiment was conducted to evaluate ammonia removal from high ammonia-containing wastewater by downflow hanging sponge (DHS) reactor used as ammonia stripping system. Synthetic deproteinized natural rubber wastewater was used for the experiment. The synthetic wastewater contains 0.2% (v/v) of ammonia and 0.1% (w/v) of urea with 10 − 11 of pH. Total volume of the DHS reactor was 5.6 L (1.7 m of height) including 1.4 L of sponge media. The experiment was conducted with 0.8 − 3.3 days of hydraulic retention time (HRT) and at ambient temperature. Based on the results of the experiment, the DHS reactor achieved 60.3% of ammonia removal with 3.3 days of HRT. In the DHS reactor, ammonia concentration and pH decreased from 1,620 to 650 mgN/L and from 10.4 to 8.1, respectively. The decrease of ammonia after 72 cm depth of the reactor was not observed. Furthermore, nitrate was confirmed in the DHS effluent corresponding approximately to 2 − 6% of removed ammonia. Therefore, it is indicated that ammonia stripping by DHS reactor can be applied as pre-treatment system for high ammonia-containing wastewater.
Particles and colloids in feedwater for reverse osmosis (RO) processes are typically removed by pretreatment to silt density index allowable levels to prevent accumulation on membranes. However, the accumulation is mostly caused due to combined biofouling-particulate accumulation and it is important to quantitatively understand particle accumulation as affected by biofilm. This study aims to determine the effect of biofilm on the accumulation of inorganic suspended solids on RO membranes. With the same kaolin concentration contained on the feedwater, the amount of inorganic material deposited was greater by 0.16 mg/cm2 when secondary effluent water was used in contrast to pure water, signifying quantitative enhancement of accumulated suspended solid (SS) on the membrane. Amount of glucose in feedwater did not result in a related increase in inorganic material since deposition seemed to be influenced by biofilm coverage on a preformed biofilm, as indicated by similar biofilm percentage coverage with and without glucose in feedwater. Micrographs indicated the preferential deposition of SS on the spacer filaments and membrane areas that were covered with biofilm. This effect of biofilm on inorganic SS accumulation will be highly useful in designing pretreatment strategies by addressing biofilm control to prevent both biofilm formation and SS accumulation.
A continuous high solid co-digestion experiment of dewatered sludge from an oxidation ditch process and waste fried tofu was conducted at 55°C in the present study. Sludge retention time was 10 days, and the mixing ratio of sludge, dry and raw fried tofu was 1:0.39:0.06 (dry weight basis). Total solids (TS) of substrate was increased gradually (30, 50, 70, 100 g/L) in the sludge digestion, while TS was increased and then decreased in the co-digestion (43.5, 72.5, 101.5, 72.5 g/L). In the sludge digestion, performance was stable when the TS was below 70 g/L (organic loading rate (OLR) was 5.9 kg-volatile solids (VS)/(m3·d)), and methane yields of sludge were 0.05–0.08 L/g-TS. In the co-digestion, biogas production significantly increased by the fried tofu addition. When total TS was increased to 101.5 g/L (OLR 8.8 kg-VS/(m3·d)), accumulation of ammonia and volatile fatty acid was observed, inhibition was indicated. Methane fermentation failed to recover when the TS was decreased to 72.5 g/L (OLR 6.3 kg-VS/(m3·d)). Results of the denaturing gradient gel electrophoresis analysis of the microbial community revealed a significant difference in the bacterial community with the fried tofu addition, while no major difference in the archaeal community was recognized.
Recently membrane bioreactors (MBRs) have been applied to municipal wastewater treatment plants. They have many advantages and the reuse of the treated water is expected for various purposes. In this study the applicability for treatment of a kitchen wastewater was examined through a MBR pilot scale experiment. In addition the MBR operational condition for the low water temperature period was also studied. The MBR experiment using the kitchen wastewater was carried out throughout the year. We prepared a newly developed flat sheet membrane made from chlorinated polyvinyl chloride hydrophilized with hydroxy-propyl cellulose, which plays a role to prevent membrane surfaces from the fouling. In the treatment of a kitchen wastewater newly developed membrane maintained the performance for one year only by performing physical cleaning. In addition it confirmed newly developed membrane after one year use kept the hydrophilicity by measuring contact angles and flux. It was observed that our developed membrane was applicable to treatment of a kitchen wastewater including the winter period.
The resistance in Escherichia coli to clinically important antimicrobial agents including fluoroquinolones and third-generation cephalosporins was investigated in the Tama river watershed to obtain the regional prevalence of the resistance to the newer antimicrobials. Among a total of 3,629 isolates, 78 strains (2.1%) were resistant to cefotaxime (probable extended-spectrum β-lactamases producers) and 76 isolates were resistant to levofloxacin, although no carbapenem-resistant strains were found. A high occurrence of the multiple resistant bacteria to different classes of newer antimicrobials was seen. The gap in the resistant ratio on the boundary between the mountainous area and urbanized area suggests that the antimicrobial resistance is a more sensitive indicator for fecal contamination than the density of E. coli. The resistant ratios of the environmental samples taken even at the middle to downstream in the watershed were lower than those of clinical isolates reported in a nationwide monitoring.
We applied excitation emission matrix-parallel factor analysis (EEM-PARAFAC) technique to ascertain the fluorophore group indicating fecal pollution from the complex nature of dissolved organic matter (DOM) in surface water of Kushiro River Basin. Covariation between relative concentrations of identified fluorophore groups and specific steroid profiles were analyzed to produce an alternate classical steroid indicator of fecal pollution by the identified fluorophore group. The fluorophore, showing fluorescent characteristics similar to those of the indole ring structure of tryptophan, was found from cattle slurry. The maximum fluorescence intensities (Fmax) of the fluorophore showed seasonal and spatial distribution similar to that of coprostanol (5β), which is known as indicator of fecal pollution. The fluorophore was widely detected in surface water of Kushiro River Basin collected from autumn through the following spring, after application of cattle slurry to pastureland. In this case, Fmax of the fluorophore showed good correlation with 5β, while during fall through spring, it is useful similar to 5β. Composition of 5β in fecal sterols is specific to the type of domestic animal. Correlation between 5β and Fmax of the fluorophore holds only in a basin that has the DOM sources of breeding beef and dairy cattle such as Kushiro River Basin.
In this study, we have modified gibbsite, one of the mineral forms of aluminum hydroxide, by calcination at 400°C (GB400) to be used as an adsorbent. Properties of pristine gibbsite and GB400 have been investigated. Adsorption of V, Sr, and Mo onto GB400 and the effect of contact time and pH in solution on the adsorption process have been investigated using the adsorption isotherms. Desorption process and the selective adsorption and desorption of the metal ions in binary or ternary solution systems have also been monitored. Adsorption isotherms for V, Sr, and Mo were fitted well using the Langmuir equation in comparison to the Freundlich equation. Adsorption equilibrium for V, Sr, and Mo were attained within 12 h, 10 − 20 min, and 10 − 20 min, respectively. These data can be well described with a pseudo-second-order model than a pseudo-first-order model. V, Sr, and Mo adsorbed onto GB400 were easily desorbed (recovered) using hydrochloric acid or sodium hydroxide solutions of different concentrations. GB400 exhibits selective adsorption and desorption capacities in binary and ternary solution systems, which indicate that GB400 could be used for the selective recovery of rare metals from ternary (complex) solution systems.
Influence of external carbon dosage for balancing denitrification kinetics for heterotrophic organisms is necessary to understand the efficiency of biological nitrogen removal from wastewater. The aim of this study was to evaluate the long term effect of ethanol dosage on heterotrophs. Three experiments were performed for 38 hours with a single dose at 1.2 mgCOD/mgTSS of food to microorganism ratio. We observed that organisms needed at least 20 hours to acclimate to ethanol based on specific denitrification rate (SDNR) and carbon to nitrate (C/N) ratio. However, for multiple dosage of ethanol for 67 hours of contact time showed that SDNR increased by more than five times compared to single dosage. In this case, the C/N ratio and anoxic yield coefficient decreased as N2O emission increased during multiple times of ethanol addition. The maximum of 4.4% of N2O emission was observed at C/N ratio of 4.38 mgCOD/mgNO3-N. It was concluded that higher influent C/N ratio for longer time contact with biomass was responsible for producing N2O gases which inhibited the yield. Thus, the possibility of using optimal ethanol dose with specific feeding time is critical to estimate the correct carbon requirement for denitrification.
Carbon dioxide (CO2) emitted from facilities such as incinerators in wastewater treatment plants (WWTPs) is an essential carbon source for indigenous microalgae, and cultivation with the CO2 is a promising energy production system for the WWTPs. In this study, CO2 addition was controlled by pH in cultures, and indoor experiments, including three reactors with the addition (pH at 7, 8, 9) and one reactor without the addition (at 10.8), were conducted to reveal suitable additional conditions for the cultivation with treated effluent. Six-month outdoor experiments were performed to investigate its effectiveness. The indoor experiments verified that not only an increase of suspended solids concentrations but also that of higher heating values to which high carbon and hydrogen content contributed were achieved by CO2 addition, represented as 170 mg/L and 21.0 kJ/g at pH 8 and 50 mg/L and 11.6 kJ/g at 10.8. The suitability of the addition at pH 8 is suggested. The outdoor experiment revealed that Scenedesmaceae and Dictyosphaeriaceae dominated with the addition at pH 8 and without the addition, respectively. Addition of CO2 at pH 8 enhanced energy production efficiency approximately from 110 to 150 kJ/(m2·d), and its effectiveness on the outdoor cultivation was verified.
Trickling filter process is focused on developing Asian countries in recent years as an alternative energy-saving wastewater treatment to conventional activated sludge systems. This paper investigated influential hydraulic operational parameters on the process performance using a nitrification reactor. The trickling filter process was expressed as 2-dimensional biofilm layers where the influent flowed to the bottom of the filter bed while oxygen was dissolved from the ambient air. The 4 m-height pilot-scale trickling filter filled with tubular plastic media (1.5 cm × 1.5 cm, 371 m2/m3-reactor volume) was installed at a municipal wastewater treatment plant in Da Nang, Vietnam. During the 2-day hydraulic stress test, the nitrogen and hydraulic loadings were changed in a step-wise manner. Focusing on the nitrification which was a dominant oxygen uptake, the process performance was dynamically simulated with a modification of IWA Activated Sludge Model (International Water Association). The effluent concentrations of dissolved oxygen and inorganic soluble nitrogenous compounds were reasonably calculated under the hydraulic loading ranging between 2.4 and 18 m/h. The reactive wetted surface area of the filter seemed to increase when high linear velocity of the fluid was applied, which resulted in the increase of volumetric biological reaction rates.
A new method for analyzing polyhydroxyalkanoate (PHA) in activated sludge based on alkaline digestion followed by high-performance liquid chromatography (HPLC) was evaluated. The effects of the concentration of NaOH, reaction time, and reaction temperature were examined using activated-sludge samples containing PHA and commercially purchased PHA. To determine PHA concentrations, 0.5 mL 2 N NaOH was added to 1 mL activated-sludge mixed liquor, and the resulting mixture was heated at 105°C in a drying oven for 1 h to convert 3-hydroxybutyrate units into 2-butenoate and 3-hydroxyvalerate units into 2-pentenoate. The mixture was then acidified with 0.5 mL of 2 N H2SO4, and the solids were removed and subsequently analyzed by HPLC. The present method gave results consistent with those obtained by the conventional method of methanolysis followed by gas chromatography. The present method can facilitate investigations of PHA in activated sludge by reducing the time and labor required for analysis and by eliminating the use of organic solvents.