The authors evaluated the energy efficiency of a novel oxidation ditch (OD) system with dual dissolved oxygen (DO) control technology through clean water tests and continuous treatment of domestic wastewater in a full-scale OD. The system maintained a constant DO gradient in the loop channel by independently controlling the aeration intensity and the circulation flow rate. Clean water tests demonstrated that a standard aeration efficiency of 1.4 - 2.1 kgO2/kWh was obtained in the OD equipped with membrane diffusers, blowers and vertical flow boosters, and these values were relatively higher than the previously reported values. The calculated standard aeration efficiency varied depending on the airflow rate and rotational speed of the flow boosters. Continuous treatment revealed that the power consumption was reduced by 67% when compared with the existing OD system. Reducing endogenous respiration, improving the standard aeration efficiency, and applying dual DO control were estimated to contribute 15%, 28% and 23%, respectively, to the total reduction of power consumption. Overall, this novel OD system showed extraordinary nitrogen removal performance with very low energy consumption.
Ultra- and micro-filtration (UF/MF) membranes have been increasingly used in a number of water separation processes. However, the popular nascent polyvinylidene fluoride (PVDF) membranes are susceptible to organic fouling and/or biofouling, which still remain as the main problem that reduces the cost-effectiveness of the processes. Recently, an innovative surface modification approach was developed which involves the doping of anhydrous and hydrated aluminum oxides (γ-alumina, boehmite and gibbsite) onto the PVDF membrane surface in an attempt to improve the membrane anti-fouling property. In this study, the anti-fouling performance of the aluminum oxide-doped membranes was evaluated, in comparison to the nascent PVDF membranes. Filtration of sodium alginate solution found that the nascent PVDF UF membrane was quite susceptible to organic fouling due to its hydrophobic nature. In contrast, organic fouling to either the γ-alumina-embedded or gibbsite-grown UF membranes was insignificant. However, during the filtration of calcium alginate dispersion, gel layer was formed on the surface of all tested UF membranes. Nevertheless, the extent of gel layer formation on the γ-alumina-embedded membrane was significantly lower than that on the nascent membrane. It appears that the growth of gibbsite particles did not help to reduce the extent of gel layer formation, which possibly resulted from the increased membrane surface roughness. With regard to biofouling, it showed that the attached bacteria per unit area were reduced with increased coverage ratio of the aluminum oxides on the UF/MF membrane surface. Although γ-alumina embedment could not completely eliminate bacterial attachment, the biofilm growth on it was largely prohibited. It seems that in situ embedment of nanoparticles on the membrane surface is sufficient to reduce common organic fouling, retard gel layer deposition and prohibit biofilm formation.
An onsite survey of heavy metal pollution in the environment, including tailings, soil, and water around Cho Dien mine was conducted. There is considerable amount of heavy metal pollutants, such as As, Cu, Cd, Pb, Zn, present at various levels in soil, surface water, and drinking water. Note that, most of the soil samples are being severely polluted with Pb, Zn, Cd and As. The results showed that 100% of soil samples contained Pb and Zn exceeding the Vietnamese standards. Tailings sample was found to contain elevated levels of these pollutants. Overall, surface water and drinking water around the mining area were found to have low As, Cd, and Cu content. Meanwhile, there have been quality problems for drinking water and surface water containing relatively high concentrations of Pb, with 45.4% and 40% of total samples exceeding the allowable standard, respectively. High concentrations of Pb were found in some water samples collected from sites close to the mining area and tailings dam. Mining wastes and tailings are sources of heavy metal pollution and may result in ecotoxicological effects on terrestrial, groundwater and aquatic ecosystems. On the other hand, the source identification of contaminants was made partially by the examination of the distribution map and also based on what other researchers mentioned.
Urban runoff usually contains significant amounts of organic and inorganic colloidal particles. Due to their high surface area and associated surface charges, these colloidal particles become a strong binding site and carriers for many contaminants found in the runoff. This paper presents a study on the physicochemical properties and behaviors of organic colloidal particles found in urban runoff under different simulated pH conditions. Four optical characterization techniques, namely (1) UV spectroscopy; (2) fluorescence spectroscopy; (3) size-exclusion chromatography with UV detector and (4) dynamic light scattering were used to examine and evaluate the colloidal properties and their behaviors. It was found that the colloidal particles under both acidic and alkaline conditions exhibited a distinct bimodal characteristic in particle-size distribution. Parallel interpretation of the four optical characterization results revealed that the influence of pH on the colloidal particles were more prominent at alkaline conditions, where an enormous growth of larger colloidal particles was observed as a result of aggregation and/or dissolution of humics and fulvic-type substances as well as biopolymers and their precursors. Results showed that the colloidal particles behave differently under acidic, neutral and alkaline conditions. This has an important implication on the water quality and immediate water treatment processes are required.
Agricultural activities of Bangladesh, being dependent on seasonal rainfall, are adversely affected by the shortage of seasonal rainfall during dry periods. Intensified drought damages due to climate variabilities have increased the urgency of proper assessment of drought in Bangladesh. Rainfall anomalies and rainfall anomaly index (RAI) were used to characterize meteorological drought scenario in Bangladesh. In addition, drought area index and percent anomaly were used to quantify drought. Analyses on rainfall intensities showed that the maximum decrease in monsoon rainfall occurred in Comilla (0.006 mm/hr). The ranges of rainfall intensity for drought condition were 0.00 - 0.29 mm/hr in pre-monsoon, 0.00 - 0.45 mm/hr in monsoon, 0.00 - 0.17 mm/hr in post-monsoon and 0.00 - 0.03 mm/hr in winter. Percentage of seasonal rainfall anomaly showed that the percentage of dry year was maximum in Jessore (42%), while it was 38% in Dhaka. Coefficient of Variation (CV), CV anomalies, and drought probability index (DPI) were used to assess rainfall reliability and drought uncertainty. The assessment on meteorological drought along with several adaptation measures found in this study will contribute to the drought management of the country.
In order to investigate the estrogenic activity profiles and quantitatively characterize the substances contributing to estrogenic activity in the river, biological and chemical analysis were applied to river water extracts. Water samples were collected throughout one year at upstream, midstream and downstream locations of the Akashi River system in Kobe, Japan. The highest estrogenic activity in river water was observed at site A-3 (5.13 × 10-12 M estradiol equivalent concentration (EEQ)) in Akashi River, which had inflow of discharge effluent from a sewage treatment plant (ESTP) immediately at the upper stream. Results of LC-MS analysis and E-screen assay from samples of A-3 and ESTP demonstrated that estrogens and estrogenic activities detected in site A-3 originated from ESTP. Of the three estrogens and six xenoestrogens analyzed in this study, di (2-ethylhexyl) phthalate (DEHP) and bisphenol A (BPA) were detected in almost all the samples but the calculated EEQ values from these xenoestrogens were below the detection limit of the bioassay. Estrone (E1) was found at sites A-2, A-3 and ESTP, while E2 was found at site A-3 and ESTP. These estrogens (E1 and E2) are the major substances contributing to the estrogenic activity of the samples. However, the EEQ values determined by E-screen assay were lower than those calculated from LC-MS analysis. In consideration of the former reports, the estrogenic activity of river water may be suppressed by estrogen antagonists. Furthermore, the estrogenic activity observed in site I-1 may be affected by some unknown chemicals in the effluent from landfill (EL).
Granular sludge was successfully cultivated under intermittent anaerobic and aerobic reaction phase strategy using synthetic textile wastewater for 72 days. The granules were developed under superficial air velocity of 2.4 cm/s in the SBR system that operated at hydraulic retention time of 8 hours. The unique feature of the granules is that they were cultivated using anaerobic granules as seeding material. The microscopic examination showed clear, smooth and spherical shape of mature granules with diameters ranging from 0.85 to 1 mm after 60 days of operation. The particle size distribution has shifted from less than 0.3 mm in the beginning to about 1 mm with some reaching 2.5 mm. The granules had good settling properties indicated by their high settling velocity reaching up to about 42 m/h and low sludge volume index (SVI) of 61 mL/g. The MLSS has also increased from 4.8 g/L to 7 g/L while the granular strength has also increased with time. During the development process, the granular sludge system was capable of treating synthetic textile dyeing wastewater containing mixed dyes with 93% of COD and ammonia removal and 56% of color removal.
This research explores the use of UV absorption and fluorescence spectroscopy for rapid monitoring of organic compounds in leachates and performs a systematic comparison of the biodegradation associated evolution of different organic compounds of leachates collected from two UK MSW landfills L1 and L2. Spectroscopic techniques are used to characterize the aromatic compounds and to study the evolution of humic, fulvic and protein like compounds which is compared with the well established organic strength estimation techniques dissolved organic carbon (DOC) and chemical oxygen demand (COD). The biodegradation of different leachates as estimated from the reduction of different organic compounds using spectroscopy show an excellent agreement with the biodegradability assessed by the conventional methods DOC and COD indicating that characterization of landfill leachates using spectroscopic methods are reliable. It is also found that leachates collected from treatment plant and phase 4 of landfill L1 (L1 (LTP) and L1 (P4) respectively) and phase 2 of landfill L2 (L2 (P2)) are less biodegradable and contain aromatic ring of more condensed form than those for leachates collected from treatment plant of landfill L2 (L2 (LTP) and L2 (FE)) which indicate a relatively rigorous treatment requirement for L1 (LTP), L1 (P4) and L2 (P2) leachates to meet the effluent standard.