Environmental Technology

Ünlu, A.; Sekerdag, N.

doi: 10.1080/09593330.2000.9618958pmid: N/A

This paper deals with the dispersion phenomena of conservative tracer materials. Rhombic arrangements are taken into account in trickling filters and a non-uniform flow condition is maintained. A general differential equation is derived and applied to describe the flow over a spherical-jet chain. A computer program aided solution method is presented. The calculation of the dispersion coefficients by using this dispersed flow model approach is shown by examples for different flow rate conditions through trickling filters.

Gabaldón, C.; Ferrer, J.; Seco, A.; Marzal, P.

doi: 10.1080/09593330.2000.9618959pmid: N/A

A steady-state model for carbon oxidation and nitrogen removal suitable for the design of wastewater and sludge suspended growth and wastewater attached growth biological processes is proposed. The model is based on the WEF-ASCE model for combined BOD5 and nitrogen oxidation activated sludge processes. Kinetic and stoichiometric coefficients have been calibrated from data of municipal wastewater treatment plants. Results of model evaluation are presented through four case studies involving full-scale wastewater treatment plants. The case studies have been selected to show the model applicability to different scenarios: from simple small plant to complex large plant or from domestic influent wastewater to major industrial contributions.

Passounaud, M.; Bollinger, J. C.; Serpaud, B.; Lacour, S.

doi: 10.1080/09593330.2000.9618960pmid: N/A

Two grafted textiles produced by the Institut Textile de France (Lyon), were examined to determine their characteristics for nitrate removal. Both weak and strong basic groups linked to textiles were used as anion-exchangers (AET). Their exchange capacity was measured as ≈ 0.6 meq.g−1, a value lower than the one determined in the case of resins. Rapid exchange kinetics was observed for both textiles. Low nitrate concentrations could be removed easily. After studying of the counter-ion influence, it appeared that nitrate removal was greater when the textiles were in the chloride form. However, the presence of other anions, such as sulphate, hydroxide and chloride could compete in nitrate removal. Selectivity gradients were determined for the weak AET as SO4 2− > NO3 − > Cl−. In the case of strong AET they were: OH− > SO4 2− > NO3 − > Cl−. Regeneration was optimal in the presence of an excess of HCl for both textiles. These anion-exchanger textiles offer an interesting and advantageous alternative for water treatment by ion-exchange technique.

Chu, H. Y.; Tam, N.F. Y.; Lam, S.K. S.; Wong, Y. S.

doi: 10.1080/09593330.2000.9618961pmid: N/A

Mangrove wetlands were effective in retaining heavy metals and nutrients from wastewater. Significantly higher concentrations of heavy metals (Cr, Cu, Ni and Zn) and total Kjeldahl nitrogen (TKN) were found in the surface soil layer (0 - 5 cm) of a mangrove tide-tank system after receiving synthetic wastewater for 16 weeks. The pollutant concentrations in NW (normal wastewater) and 5NW (5 times of normal wastewater) treated surface soils did not change significantly after flushing with clean seawater for 38 weeks (the recovery period), suggesting the pollutants retained in mangrove systems were not leached out. On the other hand, a significant reduction of heavy metals (except Ni) and TKN in surface soils receiving the strong wastewater (25 NW, 25 times of normal wastewater) was observed at the end of the recovery period. During the first 6 weeks of the recovery period, heavy metals and nutrients were detected in the effluent discharged from 25NW tank indicating that some initial washout of pollutants in mangrove soils with more metals accumulation, although their concentrations declined rapidly. The growth of Kandelia candel, a dominant mangrove plant, was not inhibited by wastewater treatment and best growth was observed in tide tanks treated with 25NW. These results suggested that the tide-tank system was effective in retaining wastewater-borne pollutants and the problem of releasing the pollutants back to the flushing seawater was not obvious. Indeed, the retained nutrients and trace elements in mangrove soils provided an extra nutrient source and supported better plant growth.

Zhou, L. X.; Yang, H.; Shen, Q. R.; Wong, M. H.; Wong, J.W. C.

doi: 10.1080/09593330.2000.9618962pmid: N/A

Dissolved organic matter (DOM) is an important component affecting the availability of heavy metals in sludge-amended soils. In this study, DOM derived from anaerobically digested dewatered sludge and sludge compost were fractionated by a macroreticular exchange resin, and characterized by Fourier Transform-Infrared spectroscopy (FT-IR) technique to evaluate their potential effects on soil metal mobility. The acid fractions of DOM in sludge and sludge compost respectively were 78% and 73%, which included hydrophilic (HiA) and hydrophobic (HoA) acids. The hydrophobic fraction of DOM increased during composting, with the hydrophobic neutral (HoN) and HoA increasing from <1 to 22% and from 38 to 52%, respectively. The relative amount of each component in the hydrophilic fraction of DOM was as follows: hydrophilic acid (HiA) >> hydrophilic base (HiB) > hydrophilic neutral (HiN). The HiA, HiB, and HiN fraction of the sludge DOM was 1.9, 6.7, and 2.2 times higher than the respective fractions of the sludge compost DOM. The FT-IR spectrum shows that the hydrophobic fraction had considerably higher aromatic acids or aromatic phenols, while the hydrophilic fraction was richer in carboxyl and polyhydroxyl groups. Sludge DOM appeared to have more C-N and C-O ligand character, possibly from organic acid, amino acid, and amines than compost DOM, especially for the HiA, HiB, and HoA fractions. Since the hydrophilic fraction of sewage sludge was higher than that of sludge compost, the addition of sewage sludge would likely have a higher ability in reducing the trace metal adsorption capacity of soils as compared to that of sludge compost.

Glasgow, L. A.

doi: 10.1080/09593330.2000.9618963pmid: N/A

The expulsion of interstitial fluid from flocs figures prominently in a wide variety of solid-liquid separation processes, particularly wastewater treatment and mineral processing. However, our understanding of floc structure, and particularly of how flocs respond to applied stress, is inadequate for some of the tasks at hand. An experimental technique has been developed in which the vertical compression of individual clay-polymer flocs in a cylinder-piston apparatus can be observed with macrovideography. The dynamics of the compression process have been modeled and the results compared with experiment; the technique has shown an ability to differentiate between floc structures formed with different polymer dosing regimens. A model of the drainage process for interstitial passageways indicates that modest-sized voids drain fairly rapidly relative to the time required for floc compression. This suggests that expulsion of fluid from passageways during compressive floc deformation generally occurs sequentially rather than simultaneously.

Wahaab, R. A.

doi: 10.1080/09593330.2000.9618964pmid: N/A

Evaluation of the elimination and the ‘ultimate’ biodegradation by aerobic microorganisms of some organic compounds applied in paper manufacturing technology was investigated. Biodegradation lines of nine organic compounds as percentage removal of chemical oxygen demand (COD) were detected over a seven day incubation. The results of the biodegradability test clearly revealed that some of the organic compounds under investigation are highly biodegradable, while others rank from fairly to even non-biodegradable. Significant biodegradation results were recorded as COD removal, for Anti-coating ester (95.0%), Basoplast 200D (85.3%) and Basoplast PR 8050(87.6%). Bleaching agent (Formamidin-sulfinic acid), Ukanol BSA and Solidurit KM demonstrate moderate biodegradation results of 62.1%, 76.2% and 69.8%, respectively. Poor biodegradation results for Hedifix M/35 (12.7%), Basazol Orange (34.9%) and Basazol Brown (29.0%) were recorded. Accordingly, appropriate caution should be taken into consideration when applying these compounds.

Costarramone, N.; Tellier, S.; Grano, B.; Lecomte, D.; Astruc, M.

doi: 10.1080/09593330.2000.9618965pmid: N/A

Definition and implementation of adapted conditions for decontamination a fluorine polluted soil, using an electrokinetic process are described. Chemical batch extractions were first performed to evaluate the efficiency of some parameters like pH, nature of reagents for fluorine removal from the soil. The results showed that fluorine mobilization in the soil studied was pH dependent. The alkaline pH was favorable to fluorine recovery. In this medium, F− was the only predominant species in solution. Three laboratory electromigration tests were subsequently performed under controlled pH conditions. The results indicated that the fluorine recovery from the soil was obtained using a simple addition of water at the cathode. In water added at the cathode allowed generation of hydroxide ions which were then transported by electromigration toward the anode, increasing pH in the soil in about 10 days. This in situ OH production has the advantage of limiting reagent addition. A pH control was then achieved at the anode (by flushing it with a dilute alkaline solution) in order to prevent an undesirable low pH resulting from generation of hydronium ions. With such conditions, the part of mobilizable fluorine was removed in less than 30 days.

Trapido, M.; Kallas, J.

doi: 10.1080/09593330.2000.9618966pmid: N/A

Advanced oxidation processes such as hydrogen peroxide photolysis, Fenton reagent and ozonation combined with hydrogen peroxide and UV-radiation were applied for the degradation of 4-nitrophenol. These processes enabled both degration 4-nitrophenol and elimination of the toxicity as the degradation by-products of advanced oxidation of 4-nitrophenol were found to be non-toxic, according to Daphnia magna acute toxicity test. Although all these processes led to the degradation of 4-nitrophenol, the Fenton reagent was found to be most promising method for the destruction of 4-nitrophenol.

Bustos, R.; Rutllant, J.

doi: 10.1080/09593330.2000.9618967pmid: N/A

Most of the air pollution episodes in Santiago (Chile) occur during the austral winter in connection with downslope easterly winds forced by upper-air troughs crossing the Andes and the associated poleward propagation of coastal lows along central Chile. During this process the subsidence inversion strengthens and lowers with a severe reduction of the ventilation factor of the city. Efforts to produce short-term forecasts of the onset and exit conditions associated with those episodes have relied mostly upon winds and temperatures measured at hilltop automatic stations located around the typical heights of the subsidence inversion over the Santiago basin. In search of alternative ways to track in real time the presence of the inversion at critical heights and strengths, the trapping of radio waves through the inversion should provide a way to monitor basin scale properties. Ray-tracing techniques to model radio signals propagating in an ‘atmospheric duct’ associated with strong subsidence inversions are discussed together with experimental results from a 65 km UHF radio link encompassing the Santiago basin at a typical height associated with air pollution episodes. It is concluded that the shape of the received signal during an air pollution episode in September 1997 reproduces the expected transition from multi-ray constructive interference to the shadow area as the inversion moves vertically. It is also demonstrated that a simple vertically-staggered set of receiving antennas could monitor the inversion drift at the onset and exit of episodic conditions once the inversion has reached the critical strength to generate an atmospheric duct.