Edward I. Stentiford

The effect of heavy metals accumulation on the chlorophyll concentration of Typha latifolia plants, growing in a substrate containing sewage sludge compost and watered with metaliferus water

Typha latifolia plants, commonly known as cattails, were grown in a mixture of sewage sludge compost, commercial compost and perlite. Four groups (A, B, C and D) were irrigated (once every 2 weeks) with a solution containing different concentrations of Cd, Cu, Ni, Pb and Zn, where in the fifth (group M) tap water was used. At the end of the 10 weeks experimental period the mean concentration of Ni, Cu and Zn in the roots and leaves of the plants in the four groups was significantly larger to that of the plants of group M. A linear regression test satisfactorily correlated the metals’ concentrations in the irrigation solutions with the metals concentration in the leaves and roots of groups A, B, C and D. The concentration of total chlorophyll, chlorophyll a (chla) and chlorophyll b (chlb) in the leaves of the developing plants was also monitored in 2 weeks intervals. Groups A, B, C and M presented an increasing concentration of total chlorophyll, with time. In group D (stronger solution), the mean total chlorophyll concentration was reduced from 1080.69 mg/g fresh weight (f.w.) in the 8th week to 715.14 mg/g f.w., in the 10th week, a probable evidence of inhibition. When statistically tested, it was suggested that there was no significant difference between the mean chlorophyll values of the groups in each set of samples, concluding that no significant toxic action was imposed in the plants by the metals. However, when similar statistical analysis was implemented in the ratios of chla and chlb, there was significant reduction of the ratios in groups D plants, suggesting some increase in chlorophyll hydrolysis due to the metals accumulation (toxic effect) in comparison with the other groups. # 2003 Elsevier Science B.V. All rights reserved.

Bioaerosol generation at large-scale green waste composting plants

Abstract Bioaerosol release from composting plants is a cause of concern because of the potential health impacts on site workers and local residents. A one-year monitoring was undertaken in a typical composting plant treating green wastes by windrowing in the open. Aspergillus fumigatus spores and mesophilic bacteria were used as monitoring parameters and were collected in a six-stage Andersen sampler impactor from the air at different locations and during different operational activities. Background concentrations of both microorganisms were generally below 1000 colony-forming units m−3 when no vigorous activity was taking place. Shredding of fresh green wastes, pile turning, and screening of mature compost were identified as the activities generating the highest amounts of both bioaerosols 40 m downwind of the composting pad. These air concentrations were ∼2 log units higher than background levels. Screening of mature compost generated lower amounts of A. fumigatus than the other two activities (an average of 1 log unit higher than background levels). Workers were identified as the main potential receptors of high bioaerosol concentrations in areas close to the composting pad, whereas no major risk for local residents was expected because the concentrations recorded at distances of 200 and 300 m downwind of the operational area were not significantly different from background levels.

Removal of heavy metals from a metaliferous water solution by Typha latifolia plants and sewage sludge compost

Typha latifolia plants, commonly known as cattails, were grown in a mixture of mature sewage sludge compost, commercial compost and perlite (2:1:1 by volume). Four Groups (A, B, C and D) were irrigated (once every two weeks) with a solution containing different concentrations of Cu, Ni, and Zn, where in the fifth (group M) tap water was used. At the end of the 10 weeks experimental period substrate and plants were dried, weighed and analysed for heavy metals. The amounts of all three metals removed from the irrigation solution, were substantial. In the roots and leaves/stems of T. latifolia the mean concentration of Zn reached values of 391.7 and 60.8 mg/kg of dry weight (d.w.), respectively. In the substrate of Group D all three metals recorded their highest mean concentrations of 1156.7 mg/kg d.w. for Cu, 296.7 mg/kg d.w. for Ni and 1231.7 mg/kg d.w. for Zn. Linear correlation analyses suggested that there was a linear relationship between the concentration of metals in the solutions and the concentration of metals in the substrates at the end of the experiment. The percentage removal of the metals in the substrate was large, reaching 100% for Cu and Zn in some groups and almost 96% for Ni in group D. The total amount of metals removed by the plants was considerably smaller than that of the substrate, due mainly to the small biomass development. A single factor ANOVA test (5% level) indicated that the build up in the concentration of metals in the roots and the leaves/stems was due to the use of metaliferous water solution and not from the metals pre-existing in the substrate. The contribution of the plants (both roots and leaves/stems) in the removing ability of the system was less than 1%.

Generation and Dispersion of Airborne Microorganisms from Composting Facilities

Bioaerosol release from organic waste treatment plants has become an important public concern because of the potential health impacts on workers and local residents. Airborne microorganisms were monitored at seven different composting facilities with different operating systems and treating a range of organic wastes. Aspergillus fumigatus and mesophilic bacteria were used as the principal monitoring parameters. The composting plants all showed levels of both airborne microorganisms in the 103 to 105cfu m–3 range in the operating area, making it advisable for the staff to use protective masks. The highest bioaerosol release occurred in the composting plant treating green waste using turned windrows, The main operational factors affecting airborne microorganism dispersion are discussed as well as the systems proposed for dispersion control. Bioaerosol release was reduced at enclosed systems through the use of biofilters, and the dispersion depended on meteorological conditions. In all cases the airborne levels 300 m downwind were similar to those measured at background locations.

Survival of faecal indicator micro-organisms in refuse/sludge composting using the aerated static pile system

Four compost piles, employing the aerated static pile system were studied with respect to pathogen inactivation. This was evaluated by means of the commonly used indicator organisms: E. coli, faecal streptococci and salmonellae. Samples from three separate sites within the piles were used, which had experienced different temperature/time profiles during composting. All three sites were located in the section of the pile just below the cover layer. E. coli, and faecal streptococci were reduced from approximately 107 org/g.ww to less than 102 org/g.ww.

Removal of Total Suspended Solids from Wastewater in Constructed Horizontal Flow Subsurface Wetlands

Abstract Subsurface horizontal flow experimental wetlands (reed beds), were designed and built based on a combination of two design methodologies, that of the WRc and Severn Trent Water plc (1996) and that of the USA, EPA (1988). Four different growing media were used with a combination of top soil, gravel, river sand, and mature sewage sludge compost, to determine the best substrate for total suspended solids (TSS) removal. Eight units were constructed, two for each growing media. One bed for each pair was planted with Typha latifolia plants commonly known as cattails. Primary treated domestic wastewater, was continuously fed to the beds for more than six months. All eight beds performed very well. The best performance was achieved by the gravel reed beds with an almost constant removal rate above 95% and an average effluent concentration of less than 10 mg/L. Soil based beds containing top soil and sand, managed to reach values of removal around 90%. The wetlands containing compost in their substrate, produced an effluent with average concentration of less than 30 mg/L and a percentage removal between 80% and 90%. As expected, there was no significant difference in the performance of planted and unplanted wetlands.

Expert Systems in Solid Waste Management

Artificial intelligence, and expert systems in particular, are an exciting and relatively new application of computers. They provide new opportunities for harnessing the scarce and often scattered pieces of valuable knowledge and experience in solid waste management which at present is in the possession of the privileged few. While conventional algorithmic programming replaced much of the sophisticated and repetitive analytical work of the solid waste practitioner, expert systems are poised to take over the no-less important tasks of the ill-structured and less-deterministic parts of the planning, design and management processes. Endeavours in other branches of engineering to utilise this new computing technology indicate that solid waste expertise in various forms has a tremendous potential to be encoded successfully in expert systems. This state-of-the-art review presents a background of expert systems technology followed by guidelines to its successful implementation in the solid waste management domain.

Assessing odour nuisance from wastewater treatment and composting facilities in Greece

The problem of odour nuisances in Greece was explored using: (a) field measurements of a range of malodorous compounds (hydrogen sulfide, ammonia, benzene, toluene, xylenes, formaldehyde, acetaldehyde, acetone, methyl-mercaptan and carbonyl sulfide) from selected wastewater treatment plants and composting facilities; and (b) questionnaires, completed by wastewater treatment plant operators, to investigate potential odour problems, the odour abatement technologies used, and potential interest and motives for adopting such technologies. The sparse information available in the literature is also exploited. Results indicate that on several occasions there was an odour problem, often stemming from the uncontrolled city sprawl, which results in mixed and often conflicting land uses. This is particularly true for wastewater treatment plants, which tend to be built close to built-up areas and highlights the importance of town planning as a tool to minimize odour problems. Measurement of odours and/or odour related gases is not commonly practised in Greece, while the odour abatement systems currently used are often considered inadequate by plant managers who do have an active interest in using more efficient and effective technologies. To our knowledge, this is the first systematic effort to monitor the odour nuisance in the country.

Heavy Metals Fractionation During the Thermophilic Phase of Sewage Sludge Composting in Aerated Static Piles

An aerated static pile system with temperature feedback control was used for the composting of sewage sludge amended with olive tree leaves in a 1:1 (SS1) and 1:2 (SS2) v/v ratio, on two different occasions. The two piles were approximate 20 m3 each of similar dimensions; 2.0 wide at the base, 1.3 m height and 11 m long. Samples were taken from the core of the piles on four occasions: day 0 (establishment), day 15, day 30 and day 60 of the thermophilic phase. Heavy metal (Cu, Ni, Pb and Zn) fractions in each of the samples were monitored using sequential extraction with H2O (for the water soluble fraction), KCL (for the exchangeable fraction), Na2EDTA (for the inorganic bound fraction), NaOH (for the organically bound fraction) and HNO3 due the significant residual fraction of these metals in both piles and in all four samplings, which reduced any losses through leaching when water was added. For Ni the water soluble and the exchangeable fractions were dominant, reaching values of 45% in SS1 and 35% in SS2, resulting in some losses into the leachates. The fraction of metals connected to the organic matter was similar for Ni in both piles, larger in SS2 for Pb than in SS1, whereas Cu and Zn presented far larger values in SS1 than in SS2. There was no common pattern of fractionation variation among the metals in each pile or when comparing both piles.

THE REMOVAL OF NH3-N FROM PRIMARY TREATED WASTEWATER IN SUBSURFACE REED BEDS USING DIFFERENT SUBSTRATES

ABSTRACT Subsurface flow experimental reed beds, were designed and built based on a combination of two design methodologies, that of the WRc and Severn Trent Water plc [3] and that of the USA, EPA [17]. Four different growing media were used with a combination of top soil, gravel, river sand and mature sewage sludge compost, aiming to determine the best substrate for ammonia removal. Eight units were constructed, two for each material. One bed for each pair was planted with Typha latifolia plants commonly known as cattails. Primary treated domestic wastewater, was continuously fed in to the bed for more than six months. The best results were achieved by the gravel reed beds with an almost constant removal rate of NH3-N above 80%. There was no significance difference on the performance of planted and unplanted reed beds.