Pilot installation for the thermo-chemical characterisation of solid wastes

The increasing production and the large variety of wastes require operators of thermal treatment units to continuously adapt the installations or the functioning parameters to the different physical and chemical properties of the wastes. Usually, the treated waste is encountered in the form of heterogeneous mixtures. The classical tests such as thermogravimetry and calorimetric bomb operate component by component, separately. In addition to this, they can analyse only small quantities of waste at a time (a few grams). These common tests are necessary but insufficient in the global waste analysis in the view further thermal treatment. This paper presents an experimental installation, which was designed and built at the CNRS Science Division, Department of Industrial Methods, Compiègne University of Technology, France. It allows the determination of waste thermal and chemical properties by means of thermal treatment. Also, it is capable of continuously analysing significant quantities of waste (up to 50kg/h) as compared to the classical tests and it can work under various conditions: The installation reproduces the process conditions from incinerators or pyrolysis reactors. It also provides complete information on the kinetics of the waste thermal degradation and on the pollutant emissions. Using different mixtures of components present in the municipal solid waste and also in the reconstituted MSW samples, we defined a series of criteria for characterising waste behaviour during the stages of the main treatment process such as: feeding, devolatilisation/oxidation, advancement, solid residue evacuation, and pollutants emission.     

Leachate recirculation effects on waste degradation: study on columns

The purpose of this study is to determine the impact of leachate recirculation on the degradation of municipal solid wastes (bioreactor concept). The study was carried out using columns containing approximately 50 kg of waste, in order to follow waste degradation over a limited time. Three types of waste were studied: fresh waste of standard composition, fresh waste of fermentable composition and some 8-yr-old waste extracted from a site in France. Measurement of the global parameters, such as chemical oxygen demand (COD), volatile acidity, alkalinity, leachate conductivity, methane potential of the wastes and biogas production monitoring (volume of CO2 and CH4 produced), were carried out. The quantity of oxydizable matter and biogas production was increased by the leachate recirculation, and the duration of the first degradation phases was reduced in all cases. Chloride, ammonium and organic pollution accumulation was observed according to the duration of recirculation. After 400 days of degradation, waste stabilization seemed to be reached for all of the recirculated columns (COD<300 mg/L O2, and methane potential reached).     

A comparison of two techniques for studying sediment desorption kinetics of hydrophobic pollutants

A comparison of two techniques (gaseous purge and vial desorption) for studying the kinetics of desorption of hydrophobic pollutants from natural sediments was conducted using identical, pre-equilibrated pollutant-sediment suspensions. Desorption profiles for the two techniques [for Lindane, Aldrin, 2,2'-dichlorobiphenyl (2,2'-DCB), 4,4'-dichlorobiphenyl (4,4'-DCB), and 2,2',6,6'-tetrachlorobiphenyl (TCB)] were then compared, based on the distribution of pollutant mass between the labile (fast) and non-labile (slow) desorption phases and the release rate constants for each phase of release. The vial desorption technique shows many practical advantages over the gaseous purge technique, including its more realistic mixing conditions, the use of an independent sample for each data point (as opposed to a calculation of a cumulative mass purged at each time point), the fact that the vials constitute a closed system and are therefore less subject to ambient contamination, and the relatively low demands of time and money for the vial technique. No consistent trends in labile rate constants or in pollutant distribution between the labile and non-labile phase were observed between the two techniques. A comparison of kinetic parameters shows much faster non-labile rate constants for the gaseous purge technique, attributed to the violent, continuous agitation employed, which likely disrupted sediment aggregates and oxidized the natural organic matter associated with the sediment. Non-labile rate constants have implications for the long-term fate of compounds adsorbed to repetitively disturbed sediments. This study suggests that the traditionally less popular vial desorption technique may yield more realistic non-labile desorption rate constants.     

Biodegradability and ecotoxicity of amine oxide based surfactants

The aerobic and anaerobic biodegradability as well as the aquatic toxicity of two fatty amine oxides and one fatty amido amine oxide were investigated. Aerobic biodegradation was evaluated using the CO(2) headspace test (ISO 14593) and biodegradation under anaerobic conditions was assessed employing a standardised batch test. The three amine oxide based surfactants tested were readily biodegradable under aerobic conditions but only the alkyl amido amine oxide was found to be easily biodegradable under anaerobic conditions. Toxicity to Photobacterium phosphoreum and Daphnia magna was evaluated. Bacteria (EC(50) from 0.11 to 11 mg l(-1)) proved to be more sensitive to the toxic effects of the amine oxide based surfactants than crustacea (IC(50) from 6.8 to 45 mg l(-1)). The fatty amido amine oxide showed the lowest aquatic toxicity.     

Heavy metals in untreated/treated urban effluent and sludge from a biological wastewater treatment plant

Background, Aim and Scope

The presence of heavy metals in wastewater is one of the main causes of water and soil pollution. The aim of the present study was to investigate the removal of Cd, Cu, Pb, Hg, Mn, Cr and Zn in urban effluent by a biological wastewater treatment, as well as to quantify the levels of As, Be, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sn, Tl, V and Zn in dewatering sludge from the Biological Wastewater Treatment Plant to Ribeirão Preto (RP-BWTP), Brazil.

Materials and Methods

Concentrations of Cd, Cr, Cu, Mn and Pb in wastewater and those of Ni in sludge were determined by atomic absorption spectrophotometry with graphite furnace atomization. Mercury concentrations in wastewater were measured by hydride generation atomic spectrophotometry, and Zn levels were determined by atomic absorption spectrophotometry using acetylene flame. In sludge, the levels of As, Be, Cd, Cr, Cu, Fe, Hg, Mn, Pb, Sn, Tl, V and Zn were determined by inductively coupled plasma-mass spectrometry.

Results

The percentages of removal efficiency (RE) were the following: Hg 61.5%, Cd 60.0%, Zn 44.9%, Cu 44.2%, PB 39.7%, Cr 16,5% and Mn 10.4%. In turn, the mean concentrations (mg/kg) of metals in dewatering sludge followed this increasing order: Tl (<0.03), Hg (0.31), Be (0.43), As (1.14), Cd (1.34), V (59.2), Pb (132.1), Sn (166.1), Cr (195.0), Mn (208.1), Ni (239.4), Cu (391.7), Zn (864.4) and Fe (20537).

Discussion

The relationship between metal levels in untreated wastewater, as well as the removal efficiency are in agreement with previous data from various investigators, It is important to note that metal removal efficiency is not only affected by metal ion species and concentration, but also by other conditions such as operating parameters, physical, chemical, and biological factors.

Conclusions

Metal values recorded for treated wastewater and sludge were within the maximum permitted levels established by the Environmental Sanitation Company (CETESB), São Paulo, Brazil.

Recommendations

There is an urgent need for the authorities who are responsible for legislation on sludge uses in agriculture of establishing safety levels for As, Be, Hg, Sn, Tl and V.

Perspectives

According to the current metal levels, RP-BWTP sludge might be used for agriculture purposes. However, for an environmentally safe use of sewage sludge, further studies including systematic monitoring are recommended. Annual metal concentrations and predicted variations of those elements in the sludge should be monitored.

     

A batch study on the bio-fixation of carbon dioxide in the absorbed solution from a chemical wet scrubber by hot spring and marine algae

Carbon dioxide mass transfer is a key factor in cultivating micro-algae except for the light limitation of photosynthesis. It is a novel idea to enhance mass transfer with the cyclic procedure of absorbing CO(2) with a high performance alkaline abosorber such as a packed tower and regenerating the alkaline solution with algal photosynthesis. Hence, the algae with high affinity for alkaline condition must be purified. In this study, a hot spring alga (HSA) was purified from an alkaline hot spring (pH 9.3, 62 degrees C) in Taiwan and grows well over pH 11.5 and 50 degrees C. For performance of HSA, CO(2) removal efficiencies in the packed tower increase about 5-fold in a suitable growth condition compared to that without adding any potassium hydroxide. But ammonia solution was not a good choice for this system with regard to carbon dioxide removal efficiency because of its toxicity on HSA. In addition, HSA also exhibits a high growth rate under the controlled pHs from 7 to 11. Besides, a well mass balance of carbon and nitrogen made sure that less other byproducts formed in the procedure of carboxylation. For analysis of some metals in HSA, such as Mg, Mn, Fe, Zn, related to the photosynthesis increased by a rising cultivated pH and revealed that those metals might be accumulated under alkaline conditions but the growth rate was still limited by the ratio of bicarbonate (useful carbon source) and carbonate. Meanwhile, Nannochlopsis oculta (NAO) was also tested under different additional carbon sources. The results revealed that solutions of sodium/potassium carbonate are better carbon sources than ammonia carbonate/bicarbonate for the growth of NAO. However, pH 9.6 of growth limitation based on sodium was lower than one of HSA. The integrated system is, therefore, more feasible to treat CO(2) in the flue gases using the algae with higher alkaline affinity such as HSA in small volume bioreactors.     

PCDD/PCDF Isomer patterns in waste incinerator flyash and desorbed into the gas phase in relation to temperature

The influence of temperature on the PCDD and PCDF isomer profiles of a municipal waste incinerator flyash and the PCDD/PCDF desorbed from the ash under an inert atmosphere was investigated using a bench-scale reactor. Exposure to temperatures of 250 degrees C and above resulted in significant changes in the distribution of isomers within most dioxin and furan congener groups. The PCDD content tended to become more evenly distributed across the range of isomers than was the case for the raw flyash, while the PCDF content became concentrated across a relatively lower number of isomers. In most cases the desorbed PCDD/PCDF were mainly mono- to tri-chlorinated, and hence had a relatively low I-TEQ value. The isomer profiles of the desorbed species were also influenced by temperature. There were some significant differences between the PCDF isomer profiles of the desorbed species and those of the treated flyashes under the same conditions, but no clear differences between the PCDD isomer profiles.     

Risk assessment of trace elements in the stomach contents of Indo-Pacific Humpback Dolphins and Finless Porpoises in Hong Kong waters

The potential health risks due to inorganic substances, mainly metals, was evaluated for the two resident marine mammals in Hong Kong, the Indo-Pacific Humpback Dolphin (Sousa chinensis) and the Finless Porpoise (Neophocaena phocaenoides). The stomachs from the carcasses of twelve stranded dolphins and fifteen stranded porpoises were collected and the contents examined. Concentrations of thirteen trace elements (Ag, As, Cd, Co, Cr, Cs, Cu, Hg, Mn, Ni, Se, V and Zn) were determined by inductively coupled plasma mass spectrometer (ICP-MS). An assessment of risks of adverse effects was undertaken using two toxicity guideline values, namely the Reference Dose (RfD), commonly used in human health risk assessment, and the Toxicity Reference Value (TRV), based on terrestrial mammal data. The levels of trace metals in stomach contents of dolphins and porpoises were found to be similar. Risk quotients (RQ) calculated for the trace elements showed that risks to the dolphins and porpoises were generally low and within safe limits using the values based on the TRV, which are less conservative than those based on the RfD values. Using the RfD-based values the risks associated with arsenic, cadmium, chromium, copper, nickel and mercury were comparatively higher. The highest RQ was associated with arsenic, however, most of the arsenic in marine organisms should be in the non-toxic organic form, and thus the calculated risk is likely to be overestimated.     

A field trial for an ex-situ bioremediation of a drilling mud-polluted site

The remediation of drilling mud-polluted sites in the Southeast of Mexico is a top priority for Mexican oil industry. The objective of this work was to find a technology to remediate these sites. A field trial was performed by composting in biopiles, where four 1ton soil-biopiles were established, one treatment in triplicate and one unamended biopile. Amended biopiles were added with nutrients to get a C/N/P ratio of 100/3/0.5 plus a bulking agent (straw) at a soil/straw ratio of 97/3. Moisture content was maintained around 30-35%. Results showed that, after 180 d, total petroleum hydrocarbon (TPH) concentrations decreased from 99300+/-23000mgTPHkg(-1) soil to 5500+/-770mgTPHkg(-1) for amended biopiles and to 22900+/-7800mgTPHkg(-1) for unamended biopile. An undisturbed soil control showed no change in TPH concentrations. Gas chromatographic analysis showed residual alkyl dibenzothiophene type compounds. Highest bacterial counts were observed during the first 30 d which correlated with highest TPH removal, whereas fungal count increased at the end of the experimentation period. Results suggested an important role of the straw, nutrient addition and water content in stimulating aerobic microbial activity and thus hydrocarbon removal. This finding opens an opportunity to remediate old polluted sites with recalcitrant and high TPH concentration.     

Comparison of calculated and measured foliar O3 flux in crop and forest species

We designed a new gas exchange system that concurrently measures foliar H2O, O3, and CO2 flux (HOC flux system) while delivering known O3 concentrations. Stomatal responses of three species were tested: snapbean, and seedlings of California black oak (deciduous broadleaf) and blue oak (evergreen broadleaf). Acute O3 exposure (120-250 ppb over an hour) was applied under moderate light and low vapor pressure deficits during near steady state conditions. The rate of stomatal closure was measured when the whole plant was placed in the dark. An adjacent leaf on each plant was also concurrently measured in an O3-free cuvette. Under some conditions, direct measurements and calculated foliar O3 flux were within the same order of magnitude; however, endogenously low gs or O3 exposure-induced depression of gs resulted in an overestimation of calculated O3 fluxes compared with measured O3 fluxes. Sluggish stomata in response to light extinction with concurrent O3 exposure, and incomplete stomatal closure likewise underestimated measured O3 flux.