Taro Urase

Insight into metabolic and cometabolic activities of autotrophic and heterotrophic microorganisms in the biodegradation of emerging trace organic contaminants

Many efforts have been made to understand the biodegradation of emerging trace organic contaminants (EOCs) in the natural and engineered systems. This review summarizes the current knowledge on the biodegradation of EOCs while having in-depth discussion on metabolism and cometabolism of EOCs. Biodegradation of EOCs is mainly attributed to cometabolic activities of both heterotrophic and autotrophic microorganisms. Metabolism of EOCs can only be observed by heterotrophic microbes. Autotrophic ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaeal (AOA) cometabolize a variety of EOCs via the non-specific enzymes, such as ammonia monooxygenase (AMO). Higher biodegradation of EOCs is often noted under nitrification at high ammonia loading rate. The presence of a growth substrate promotes cometabolic biodegradation of EOCs. Potential strategies for enhancing the biodegradation of EOCs were also proposed in this review.

The characteristics of enriched nitrifier culture in the degradation of selected pharmaceutically active compounds

The biodegradation of 10 selected pharmaceuticals by enriched nitrifier cultures with ammonia oxidizing activity of 30mg NH(4)-N/gMLVSSh was investigated under various initial operating conditions such as in the presence of different growth substrates and inhibitors. The enriched nitrifier culture showed higher degradation of the target pharmaceuticals than the conventional activated sludge. The degradation efficiency of persistent pharmaceuticals such as clofibric acid (CA), diclofenac (DCF), carbamazepine (CBZ), and propyphenazone (PPZ) was increased with the increase in the ammonium concentration. A higher removal efficiency of CA, DCF, CBZ and PPZ was obtained when organic substrates were added. The contribution of autotrophs and heterotrophs in the biotransformation of the pharmaceuticals by the enriched nitrifier culture was successfully estimated by the addition of inhibitors. Experimental results showed that the high degradation of IBP and partial degradation of other selected pharmaceuticals were observed in the presence of allylthiourea (ATU), an ammonia monooxygenase inhibitor, reflecting the activity of heterotrophic bacteria, while the results with and without ATU addition showed that the contribution of the nitrification in the degradation of most pharmaceuticals was also dominant. The results suggest that nitrification can enhance the biotransformation of pharmaceutical substances.

Effect of pH on rejection of different species of arsenic by nanofiltration

Arsenic in drinking water attracts attention because some of the drinking water resources contain considerable concentration of arsenic to cause adverse health effects. The application of nanofiltration (NF) to drinking water treatment for arsenic removal was examined with negatively charged NF membranes. Experiments were conducted with ground water to which arsenate, arsenite and dimethyl arsinic acid (DMMA) were added. The concentrations of three different species were measured by the ion chromatography-inductively coupled plasma-mass spectrometry (IC/ICP/MS) method by which speciation and quantification of arsenic compounds with high sensitivity is possible at the same time. Arsenate rejection was almost steady, while rejection of arsenite increased with pH. Compared to the rejection of chloride ion, arsenic compounds except DMMA generally gave lower rejection. The reason for rejection change with pH was explained by the extended Nernst Planck equation in which chemical equilibrium of arsenic compounds was taken into account.

Effect of pore structure of membranes and module configuration on virus retention

We measured virus retention by many types of membranes including microfiltration membranes, ultrafiltration membranes and nanofiltration membranes. We succeeded in evaluating quantitatively virus retention in a very high retention range by employing coliphage Qβ and T4 as model viruses. Qβ, which is the smaller virus in this study, penetrated all tested pieces of ultrafiltration membranes and nanofiltration membranes, though the retention was very high such as in the range of 99-99.9999%. The analysis of the polyethylene glycol retention data has shown that the leakage of viruses is caused by abnormally larger pores which are not included in the main pore size distribution. The diameter of the abnormal pores was estimated from the results of retention of different coliphages. The leakage of Qβ was also observed in the case of inorganic ceramic ultrafiltration membranes, but T4, which is larger than Qβ, cannot penetrate them. Some types of microfiltration membrane have shown higher retention than ultrafiltration membranes and nanofiltration membranes. This suggests the possibility that we can develop high virus retention membranes with low filtration resistance.

A critical review on characterization strategies of organic matter for wastewater and water treatment processes

The presence of organic matter (OM) in raw wastewater, treated wastewater effluents, and natural water samples has been known to cause many problems in wastewater treatment and water reclamation processes, such as treatability, membrane fouling, and the formation of potentially toxic by-products during wastewater treatment. This paper summarizes the current knowledge on the methods for characterization and quantification of OM in water samples in relation to wastewater and water treatment processes including: (i) characterization based on the biodegradability; (ii) characterization based on particle size distribution; (iii) fractionation based on the hydrophilic/hydrophobic properties; (iv) characterization based on the molecular weight (MW) size distribution; and (v) characterization based on fluorescence excitation emission matrix. In addition, the advantages, disadvantages and applications of these methods are discussed in detail. The establishment of correlations among biodegradability, hydrophobic/hydrophilic fractions, MW size distribution of OM, membrane fouling and formation of toxic by-products potential is highly recommended for further studies.

Carbon catalyzed supercritical water oxidation of phenol

Abstract Activated carbon was employed as a novel catalyst for supercritical water oxidation of phenol. High-concentrations of phenol were treated in supercritical water at 673 K and 25 MPa with an equivalent amount of oxygen in a reactor packed with activated carbon. Although activated carbon itself was oxidized in the reaction field, its weight decrease was sufficiently slow for its catalytic effect on phenol oxidation to be observed. The catalytic effect of activated carbon consisted of an enhancement of the reaction rate, a decrease in the tarry product yield, and an increase in the gas yield. Under the condition used in this study, 65% of oxygen delivered into the reactor was effectively used for phenol oxidation while only 39% of oxygen was used when no catalyst was applied. This report is the first to indicate the catalytic effect of carbonaceous materials on supercritical water oxidation, and it demonstrates that supercritical water oxidation using lower operation temperatures and inexpensive carbon catalysts may be possible.

Organic stabilisation and nitrogen removal in a membrane separation bioreactor for domestic wastewater treatment

Abstract Organic stabilization and nitrogen removal wore investigated using a hollow fibre membrane separation bioreactor of 62 I volume. The process employed was direct solid-liquid separation by the hollow fibre membrane inside an activated sludge aeration tank. By providing highly turbulent conditions within the separation zone and incorporating a jet aerating installation inside the membrane module, sludge accumulation on the membrane surface and inside the module can be reduced. Permeate flux obtained after 330 days of operation was 0.2 m/d under intermittent auction. A high degree of organic stabilisation was obtained in the system without sludge wastage except for sampling purposes. Continuous and intermittent aeration modes were investigated. Average effluent COD concentrations of 20.8 and 16.5 mg/I were observed during continuous and intermittent aeration, respectively. The degree of nitrification depended on the DO concentration of the mixed liquor during the aerating period. Introduction of intermittent aeration enhanced total nitrogen removal up to 80% or more by simultaneous nitrification and denitrification, resulting in an average value of 4.9 mg/I of total nitrogen in the effluent. Increasing the DO in the aerating period from 1.5 – 2 mg/I to 4 – 5 mg/I increased nitrogen removal to more than 90%. Rejection of 4 – 6 log virus concentration by a gel layer formed on the membrane surface was also observed.

Supercritical water oxidation of high concentrations of phenol.

Decomposition of phenol at a concentration as high as 2 wt.% was effected by supercritical water oxidation at 25 MPa. Reaction temperatures ranged from 623-723 K and residence times were varied from 6.5 to 26 s. Oxygen was added in an equivalent amount to investigate reaction intermediates. The degree of phenol decomposition and reaction product were measured. Although tarry material production was observed, phenol decomposition conversion was predicted well by the reaction rate equations developed by previous researchers who conducted experiments at lower concentrations. Difference from low concentration phenol oxidation was found in the reaction product distribution and tarry material production. One possible explanation for this result is that the initiation of phenol decomposition is the same regardless of phenol concentration but that the succeeding radical reactions are different. The additive reaction between aromatic compounds was enhanced by high phenol concentration.

Role of nitrification in the biodegradation of selected artificial sweetening agents in biological wastewater treatment process.

The biodegradation of the six artificial sweetening agents including acesulfame (ACE), aspartame (ASP), cyclamate (CYC), neohesperidindihydrochalcone (NHDC), saccharin (SAC), and sucralose (SUC) by nitrifying activated sludge was first examined. Experimental results showed that ASP and NHDC were the most easily degradable compounds even in the control tests. CYC and SAC were efficiently biodegraded by the nitrifying activated sludge, whereas ACE and SUC were poorly removed. However, the biodegradation efficiencies of the ASs were increased with the increase in initial ammonium concentrations in the bioreactors. The association between nitrification and co-metabolic degradation was investigated and a linear relationship between nitrification rate and co-metabolic biodegradation rate was observed for the target artificial sweeteners (ASs). The contribution of heterotrophic microorganisms and autotrophic ammonia oxidizers in biodegradation of the ASs was elucidated, of which autotrophic ammonia oxidizers played an important role in the biodegradation of the ASs, particularly with regards to ACE and SUC.

Emission of volatile organic compounds from solid waste disposal sites and importance of heat management

The emission of volatile organic compounds (VOCs) from a solid waste disposal site for municipal solid wastes was quantified. The VOCs contained in the landfill gas taken at the site were benzene, toluene, xylenes, ethyl benzenes, and trimethyl benzenes, while the concentrations of chlorinated compounds were very low. The concentration of benzene in the landfill gas samples ranged from below the detection limit to 20 mg m—3, and the ratio of benzene to toluene ranged from 0.2 to 8. The higher concentrations of VOCs in landfill gas and in leachates were observed with the samples taken at high temperature areas of the target site. Polystyrene plastic waste was identified as one of the sources of VOCs in solid waste disposal sites at a high temperature condition. The appropriate heat management in landfill sites is an important countermeasure to avoid unusually high emission of VOCs because the heat generated by the biodegradation of organic solid wastes may promote the release of VOCs, especially in the case of sites which receive both biodegradable and plastic wastes.