Environmental Technology

Teer, J. E.; Leak, D. J.; Dudeney, A.W. L.; Narayanan, A.; Stuckey, D. C.

doi: 10.1080/09593332208618165pmid: N/A

The effect of treatment of an acidic, high sulphate/iron bearing, oxalate wastewater on pre-formed granule composition and structure in an upflow anaerobic sludge blanket (UASB) reactor was studied. The results indicated that this wastewater did not lead to the formation of new granules in a pre-seeded reactor. Ferrous precipitates which accumulated at the base of the reactor acted as a surface for adsorption of bacterial cells, and a majority of the substrate degradation occurred in this lower region. The presence of Desulfosarcina on the precipitate surface confirmed the sulphidogenic nature of the system, and these organisms outcompeted the methanogens present. After 18 months of operation compressed ellipsoidal granules were identified in the upper layers of the sludge bed, and these were proposed to be the original inoculum granules following displacement from the reactor bed and compression caused by precipitate build up.

Hasar, H.; Cuci, Y.

doi: 10.1080/09593332208618172pmid: N/A

Activated carbon was prepared from almond husk by activating with and without H2SO4 at different temperatures. The ability of the activated carbon to remove some metal ions from aqueous solutions by adsorption has been investigated under several conditions such as carbonisation temperature of husk, concentration of metal ions, contact time, and adsorbent dosage. Optimum contact time was found to be 180 minutes for an initial concentration of 100 mg l− at 5 g of adsorbent per 100 ml. The results showed that effective metal ions on the activated carbon was obtained by adding H2SO4 at 700 °C at the optimal conditions, the removal of Cr(VI), Cd(II), and Cu(II) were found to be 94.4, 93.7, and 94.7%, respectively. The Freundlich constants were calculated at differential initial concentrations under optimal conditions.

Jahren, S. J.; Ødegaard, H.

doi: 10.1080/09593332208618171pmid: N/A

Moving bed biofilm reactors were used for the thermophilic (55°C) anaerobic-aerobic treatment of a constructed high strength wastewater based on molasses. The anaerobic reactors were started with mesophilic inoculum, while the subsequent aerobic reactors were started without inoculation. The total amount of anaerobic biomass (suspended and attached) in the reactors stabilised at around 3 g VSS l−1. Substrate utilisation rates up to 4.2 kg soluble chemical oxygen demand (SCOD) (kg VSS·d)−1 were obtained at loading rates to the anaerobic biomass up to 16.4 kg SCOD (kg VSS·d)−1. Volumetric removal rates up to 7.6 kg SCOD m−3d−1 were achieved at loading rates up to 30 kg SCOD m−3d−1 in the anaerobic reactors. The maximum loading capacity however, was not evaluated during the study. Average sludge yields of 0.25–0.28 kg VSS (kg SCODremoved)−1 were achieved in the anaerobic reactors. The total amounts of aerobic biomass varied between 1.1 and 2.5 g VSS l−1. A maximum aerobic substrate utilisation rate of 4.6 kg SCOD (kg VSS·d)−1 was achieved at an aerobic biomass loading rate of 18.4 kg SCOD (kg VSS·d)−1. Volumetric removal rates up to 6.8 kg SCOD m−3d−1 were achieved at loading rates up to 27 kg SCOD m−3d−1 in the aerobic reactors. The maximum obtainable removal rates per biomass or volume were not reached during the study.

Choi, S. J.; Seo, E. J.; Shin, W. S.

doi: 10.1080/09593332208618168pmid: N/A

Laboratories studies were conducted for the removal of Cu(II) from aqueous solution using adsorbing colloid flotation with Fe(OH)3. The effects of pH, surfactant (sodium lauryl sulfate), and foreign ions (NO3 −, SO4 2−) on the removal efficiency of Cu(II) were investigated. Sodium lauryl sulfate was efficient as a surfactant for the removal of Cu(II) and the optimum pH was found at 8.0. Foreign anions highly inhibited Cu(II) removal efficiency. This limitation of foam flotation on Cu(II) removal at high ionic strength may overcome by the aid of activators. The applicability of activators to improve Cu(II) removal efficiency of foam flotation was verified experimentally. The adsorption and separation mechanisms for the removal of Cu(II) are discussed. The role of activators on Cu(II) removal is also discussed.

Gulsen, H.; Turan, M.; Altay, A.

doi: 10.1080/09593332208618174pmid: N/A

The wastewater treatment systems of a city in Turkey differ from each other depending on various factors such as population, economy, wastewater characteristics, topography, climatic conditions, urbanisation and cost of land. The construction and operation of the stabilisation ponds in all cities of Turkey are very easy due to the cheaper cost of the land and hot and mild climates. In this study, a computer model based on the Wehner-Wilhelm equation, developed by Thirumurthi, is used and for this application; first-order reaction rate (kp) and dimensionless dispersion coefficient (D) must be determined. Also, some parameters such as temperature, solar radiation, organic loading, altitude, turbidity, and hydraulic retention time are also required. The BOD5 removal in the winter for 2m of pond depth was found 50%, and 52%, in the southern region (Sanliurfa), the northern region (Samsun), and the western region (Balikesir), respectively. No result could be given for the eastern region (Erzurum) in Winter, since wastewater in the pond was frozen. Generally, the BOD5 removal was found to be 90-92% in the Summer for all provinces, and also 55-70% in the southern region, and 40-55% in the northern region in Winter during the 20 days of retention time when dimensionless dispersion coefficient and oxygenation factor are 0.2 and 1.5, respectively. The optimum effluent quality of the pond was obtained as 15-25 days of the retention time, 1-2 m of pond depth, and 0.2 dimensionless dispersion coefficient.

Alam, M. G. M.; Tokunaga, S.; Maekawa, T.

doi: 10.1080/09593332208618166pmid: N/A

Laboratory batch experiments were conducted to develop an environment-friendly and cost-effective technique for the treatment of selenium contaminated soils. A yellow brown forest soil was artificially contaminated with sodium selenite (Na2SeO3) and used as a model contaminated soil sample. Among various potassium and sodium salts, potassium phosphate exhibited a pronounced effect in extracting selenium, attaining more than 55% extraction in the pH range of 4 to 6, with minimum damage to the soil properties. Based on the sorption selectivity between phosphate and selenite, an exchange mechanism is proposed for the extraction of selenium from soil by phosphate. The results of sequential extraction show that phosphate is effective in extracting selenium, NH4F-extractable and NaOH-extractable fractions. The CH3COOH-extractable and residual fractions were poorly extracted by phosphate. Selenium was most efficiently extracted at 40°C with a 300 mM (pH 6) phosphate solution.

Watanabe, H.; Takagi, K.

doi: 10.1080/09593332208618167pmid: N/A

A simulation model for predicting pesticide concentrations in paddy water and surface soil (PCPF-1) was developed. The PCPF-1 model simulates the fate and transport of pesticide in paddy water and 1cm deep oxidative paddy surface soil layer, or the pesticide source layer (PSL). The model considers the pesticide fate and transport processes in paddy water such as dissolution of pesticide in paddy water compartment, pesticide transfer by desorption from the PSL, dilution by precipitation and irrigation, concentration from evaporation and transpiration, and dissipation by biochemical and photochemical degradation. In the PSL compartment, adsorption in soil, pesticide transport though percolation of paddy water, and pesticide dissipation by biochemical degradation are considered. The model program was coded using Visual Basic for Applications as a Macro in Microsoft Excel that includes data sheets of daily water balance and daily UV-B radiation received on paddy water. The model behavior and sensitivity analysis was conducted by using field data of daily water balance and UV-B radiation obtained at the experimental paddy rice field at National Institute of Agro-Environmental Sciences (NIAES), Ibaraki, Japan in 1988. Simulated pesticide concentrations in paddy water and PSL decreased exponentially with time. PCPF-1 successfully simulated oscillating pesticide concentrations in paddy water that affected by abrupt dilution from irrigation and precipitation and pesticide transfer from PSL. PCPF-1 indicated potentials to be a tool for investigating the pesticide fate and transport processes. The model validation using experimental data will be discussed in the concurrent paper.

Watanabe, H.; Takagi, K.

doi: 10.1080/09593332208618169pmid: N/A

A simulation model for predicting pesticide concentrations in paddy water and surface soil (PCPF-1) was validated with the result of field monitoring data of pretilachlor dissipation in experimental paddy rice field at National Institute of Agro-Environmental Sciences (NIAES), Ibaraki, Japan in 1998. Parameter values were determined from laboratory and field experiments. Environmental conditions and pesticide concentrations in experimental rice paddy plot at NIAES were monitored after the herbicide application for 52 days in 1998. Pesticide concentrations in paddy water and 1cm deep surface paddy soil sampled at 1, 3, 7, 14, 21, 28, 35 (water only), 42 and 49 days after the herbicide application were measured using gas chromatography with nitrogen/phosphorus detector (NPD-GC). The PCPF-1 model successfully simulated the drastic decline of pretilachlor concentrations in paddy water during the first week. Although the prediction of pesticide concentrations in paddy water during the mid-period of the simulation was over estimated, PCPF-1 prediction had good agreement with observed data of pretilachlor concentrations both in paddy water and surface soil for the first 10 days and last 20 days of simulation. For the pretilachlor dissipation in paddy field, pesticide desorption from paddy soil to paddy water was the key process controlling the rate of the pesticide dissipation. PCPF-1 has potential to be a beneficial tool for investigating the pesticide fate and transport processes as well as for controlling pesticide transport from the paddy field that affecting the both surface and ground water.

Sanin, D.; Vesilind, P. A.

doi: 10.1080/09593332208618170pmid: N/A

In an attempt to identify the bioflocculation mechanisms, this study examines the role of calcium ions in flocculation of activated sludge. Two calcium specific chelants, ethylenebis (oxyethylenenitrilo) tetraacetic acid (EGTA) and sodium hexametaphosphate (HMP) are used to extract calcium ions. Both chemicals successfully extract the calcium ions from sludge structure, which is confirmed either by an increase in solution calcium concentration or by a decrease in calcium concentration in the sludge solid matrix. When calcium ions are removed from sludge, the physical properties of sludge change significantly. Filterability decreases, while both the turbidity of the supernatant and the solution carbohydrate concentration increase. The decrease in filterability and increase in turbidity indicate a floc breakup, and the increase in solution carbohydrate concentration gives evidence of the release of extracellular polymeric materials from the sludge floc structure. Application of both complexing agents (EGTA and HMP) creates similar changes in sludge properties. A sludge floc model is proposed which suggests that calcium ions help form colonies from individual microorganisms interacting with microbial extracellular polymers; following this they can further take part in bridging the microbial colonies together to form flocs. These interactions are believed to be among important biofloc formation mechanisms.

Anderottola, G.; Canziani, R.; Foladori, P.; Ragazzi, M.; Tatano, F.

doi: 10.1080/09593332208618173pmid: N/A

In this paper results of a laboratory-scale experimentation on anaerobic fermentation of the organic fraction of municipal solid wastes (OFMSW) are presented. The aim of the experimentation was the evaluation of the production of readily biodegradable COD to be used in biological nutrient removal (BNR) plants. A 3.5 l glass reactor was built and the process was run under mesophilic conditions (32°C) without pH control. A batch test and five runs at different hydraulic retention times were performed, at 1.5, 3, 4, 5, and 6 days, respectively. An intermittent step-feed strategy was adopted. The feeding material came from the selective collection of municipal solid wastes, and was shredded and diluted with tap water. The kinetics of the hydrolytic process has been characterised by two parameters. The kinetic model has been related to the hydraulic retention time and can be used for design purposes.