Yutaka Terashima

Removal of dissolved heavy metals by chemical coagulation, magnetic seeding and high gradient magnetic filtration

Abstract A rapid and highly efficient treatment process for waste waters containing heavy metals was investigated by combining the processes of chemical coagulation, magnetic seeding and high gradient magnetic filtration (HGMF). Chemical coagulation was performed with ferric chloride (FeCl3), sodium sulfide (Na2S) and FeCl3, or calcium polysulfide (CaSx, x ≒ 4) and FeCl3. Magnetite was used as seeding material, to whose surface non-magnetic particles adhere. The removal tests of cadmium was performed first by varying the pretreatment conditions, such as the amount of each additive, order and time interval of addition, pH and other factors. Consequently, the desirable conditions to establish such a high removal efficiency, close to 100%, were obtained by batch experiments for each of the combined processes. Based on the above results, removal of heavy metals, including mercury, in the gas scrubbing waste water from a municipal solid waste incineration plant, was examined by the process consisting of the coagulation with CaSx and FeCl3, the magnetite seeding, and HGMF. A removal efficiency high enough to assure the effluent standards of Japan was established by monitoring the reaction in this process using a sulfide ion electrode. The CaSx added to the feed water was regenerated in a purity of nearly 100%. Almost all of the magnetite used was also recovered. About 70% of heavy metals on the magnetite was removed simultaneously.

Modelling of the Simultaneous Removal of Organic Substances and Nitrogen in a Biofilm

A mathematical model of the simultaneous removal of organic substances and nitrogen compounds in a biofilm reactor was developed, taking account of the relationships between oxidation, nitrification, denitrification, and mass transport. The model consists of a set of simultaneous mass balance equations for organic substances, ammonium nitrogen, oxidized nitrogen, oxygen, and alkalinity within the biofilm, and another set of transport equations for these substances within diffusion layer of the biofilm. Synthetic dual and triple Monod-type kinetics describing, respectively, oxidation, and nitrification and denitrification were incorporated into the mass balance equations. The model was evaluated based on experimental data and the computer simulations. This model successfully explained the mechanism of simultaneous removal and the effects of bulk concentrations of organic substances, DO, ammonium nitrogen, and alkalinity on simultaneous removal in a submerged biofilm reactor.

Chlorine stable isotope measurements of chlorinated aliphatic hydrocarbons by thermal ionization mass spectrometry

Abstract An improved method for chlorine isotopic analysis using thermal ionization mass spectrometry (TIMS) of Cs2Cl+ has been investigated. The δ 37 Cl values (parts per mil deviations from the standard seawater 37 Cl / 35 Cl ratio) for 10 commercial chlorinated aliphatic hydrocarbons (CAHs), provided by six suppliers are presented. The CAHs were treated with a sodiumbiphenyl reagent. The liberated chloride ions were converted to CsCl and their isotopic compositions were determined by TIMS. Replicate analysis of the CAHs gave an external precision of 0.1–0.4‰ (1σS.D.). As each compound and each supplier has a distinctive δ 37 Cl value (δ 37 Cl values: −5.0 to +2.9‰), Cl isotope data can be used to trace a specific source of pollutants in the subsurface environment. Trichloroethene (TCE) and tetrachloroethene (PCE) were extracted from aqueous solutions with toluene and their chlorine isotope compositions were analyzed. The solvent extraction method presented here may be applicable to the analysis of actual contaminated water samples. Chlorine atoms were recovered as inorganic chloride from unsaturated chlorinated aliphatic compounds (TCE and PCE) by KMnO4 oxidation. However, the saturated compounds were resistant to KMnO4 oxidation. The isotopic compositions of the recovered chloride ion were then determined by TIMS. It is suggested that such compound-specific isotopic analyses may give information about the past record of each contaminant.

Optimum sampling of municipal solid wastes

Abstract Quartering, random sampling, stratified sampling and cluster sampling methods are evaluated for precision and efficiency in the analysis of municipal solid wastes (MSW). The optimum method for sampling MSW is proposed and related to the object of the sampling. The main results are as follows: 1. 1. Based on observations made on the movement of tracers, the mixing stage in the quartering method can be done accurately if the weight of MSW is less than about 50kg. 2. 2. The more separation that is carried out in the quartering, the larger the relative error of the composition. However, the error is smaller if MSW is cut into smaller pieces before quartering. 3. 3. The relative error in the quartering process can be expressed by normal distribution. This probability model gives the relationship between the precision of estimation (relative error) and sample weight. 4. 4. The same relationship is also obtained with random sampling, stratified sampling and cluster sampling. 5. 5. If bulk density is used as a stratified variate, stratified sampling becomes an effective method for estimating the water content, low calorific value and several components of MSW.

Determination of dissolved oxygen limitation in aerobic biofilm reactors

Abstract The concentration of dissolved oxygen (DO) strongly influences the performance of aerobic biofilm reactors because organic oxidation is limited by the availability of oxygen. However, it is not necessary to maintain a high DO level in the reactors in order to overcome this limitation. Excessive aeration wastes energy. Therefore, the determination of the onset of DO limitation against organic substrate removal in aerobic biofilm reactors is important for their effective operation. This study is aimed at developing an expression to determine the onset of DO limitation and hence to control the aeration system. The expression developed is as follows: C b b ·( D ws D wc )·S b , where Sb and Cb are the bulk concentrations of organic substrate and DO, respectively; Dws and Dwc are the diffusion coefficients of organic substrate and oxygen in the reactors respectively; and Rb is an overall ratio of oxygen consumption to organic substrate removal in the reactors. The latter is the key parameter in the equation, and is determined by the characteristics of the substrate, biofilm, and reactor. In order to measure the value of Rb, the authors have developed a micro-biofilm reactor. The value of Rb was determined to be 0.13 (mg O2 mg−1 CODcr) for glucose removal with this reactor. The equation has, subsequently, been verified with data from batch and continuous experiments.

NEW INDEXES TO EVALUATE SUBSTRATE FEED AND AERATION IN THE ANAEROBIC/AEROBIC SEQUENCING BATCH ACTIVATED SLUDGE PROCESS

ABSTRACT In this study, several operation pattern indexes (OPIs) were proposed for the evaluation of operating conditions of the anaerobic and anoxic, and oxic sequensing batch activated sludge process (A/0 SBAS process), and reasonable conditions for the nitrogen and phosphorus removal and sludge bulking control were discussed based on the OPIs and the results of bench scale experiments of the A/0 SBAS process under various conditions. The main conclusions are as follows: For the efficient removal of both nitrogen and phosphorus, and for the improvement of sludge settleability, substrate feeding under nonaerated conditions is a prerequisite. For more effective nitrogen removal, intermittent (multiple) feeding is necessary. For more effective phosphorus removal and the improvement of sludge settleability, however, single and instantaneous feeding is needed.

EVALUATION OF CONCRETE WASTE RECYCLING FROM ENVIRONMENTAL ASPECTS

コンクリートがらの路盤材用再生砕石としてのリサイクルを対象として, 環境面からLCA的な評価を行い, 次の結論を得た. 1) コンクリートがらを路盤材用再生砕石としてリサイクルすることは, 廃棄物を抑制するのみならず, 別の多くの環境負荷も低減する. ただし, 再生工場への輸送距離が処分場への輸送距離以上になる場合には、この限りではない. 2) リサイクルケースでさらに負荷を低減する方策としては, 破砕の前処理にかかる軽油の使用量を削減することが考えられる. また, CO2, SOx, NOxの削減については, 輸送距離を考慮することが重要である.

Analysis and Estimation of the Consumption of Goods Related to Waste Generation

廃棄物の発生予測および制御を可能とするには, 発生源における発生過程の構造を定量的に知ることが必要である。本論文では, 都市廃棄物の発生源の主要部分である一般家庭について, 家庭における廃棄物発生と密接な関係があると考えられる消費財消費に着目した。統計資料情報に基づいて消費財の消費実態を検討し, 消費財消費に影響を及ぼす要因として世帯属性を取り上げた。そのうち「年間収入」「世帯人員」「世帯主年齢」という3種類の世帯属性を用いて統計的手法により家計消費の構造を解析し, 消費財の分類別消費予測式を作成するとともに, 世帯属性による家計消費予測を試みた。その結果, 消費統計資料の統計的精度によって予測精度のばらつきはあるものの, かなりの精度で短期的予測が可能であることが明らかになった。