Methane and carbon dioxide emission in a two-phase olive oil mill sludge windrow pile during composting.

The aim of this work was to make some preliminary evaluations on CO(2) and CH(4) emissions during composting of two-phase olive oil mill sludge (OOMS). OOMS, olive tree leaves (OTL) and shredded olive tree branches (OTB) were used as feedstock for Pile I and Pile II with a 1:1:1 and 1:1:2v/v ratio, respectively. Each pile was originally 1.2m high, 2.0m wide and approximately 15.0m long. Four 500 ml volume glass funnels were inverted and introduced in each pile, two in the core (buried 50-60 cm from the surface) and two near the surface under a thin 10-15 cm layer of the mixture. Thin (0.5 cm diameter) plastic, 80 cm long tubes were connected to the funnels. A mobile gas analyser (GA2000) was used to measure the composition (by volume) of O2, CO2 and CH4 on a daily basis. The funnels were removed prior to each turning and reinserted afterwards. From each pair of funnels (core and surface) of both piles, one was kept closed between samplings. Two way ANOVA was used to test differences between piles and among the tubes. Post hoc Tukey tests were also used to further investigate these differences. There was a significant difference (at p<0.001) in the two piles for all three gases. The average concentrations of O2, CO2 and CH4 in Pile I, from all four funnels was 16.86%, 3.89% and 0.25%, respectively, where for Pile II the average values were 18.07%, 2.38% and 0.04%, respectively. The presence of OOMS in larger amounts in Pile I (resulting in more intense decomposing phenomena), and the larger particle size of OTB in Pile II (resulting in increasing porosity) are the probable causes of these significant differences. Samples from open funnels presented lower, but not significantly lower, O2 composition (higher for CO2 and CH4) in comparison with closed funnels in both depths and both piles. Not significant were also the different mean gas compositions between core and surface funnels in the same pile.

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.

Bioaerosol generation at large-scale green waste composting plants.

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 approximately 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.

Sanitary aspect of using partially treated landfill leachate as a water source in green waste composting.

Shredded green wastes were composted in windrows, at the Harewood Whin landfill, near the city of York, in West Yorkshire, UK. Landfill leachate were added twice during the second and fourth week of the process in two piles. One pile was turned once every week for eight weeks and the other was turned twice, during the same period. Each time approximately, 2 m3 of leachate was added, into each pile. The two piles each contained about 45 m3 of shredded green waste. The effect of adding leachate on the sanitisation of the green waste during composting, was evaluated based on the changes in the levels of faecal coliforms and faecal streptococci. The results suggested that using leachate as the moisture source had no significant effect (tested with two factors ANOVA test) on the sanitisation process when compared with two similar piles, used as the control, for which tap water was used for moisture addition. In all four piles sanitisation was almost complete and below the acceptable levels. Additionally, the results indicated that there was no significant effect on the sanitisation process of the turning frequency.

Biofiltration at composting facilities: effectiveness for bioaerosol control.

Biofiltration was evaluated as a method to control the airborne microorganisms released at composting facilities. Seven commercial composting plants were selected for this study because of their different operating conditions and biofilter designs. In all plants, the biofilters were originally designed for odor control. The concentrations of both Aspergillus fumigatus and mesophilic bacteria were measured in the air stream before and after passing through the biofilters and compared with the background concentrations in the surrounding area. Results showed that biofiltration achieved an average reduction greater than 90% and 39% in the concentrations of A. fumigatus and mesophilic bacteria, respectively. In all the plants, the airborne A. fumigatus concentration after the biofilter was lower than 1.2 x 10(3) cfu m(-3), independent of the inlet concentration, whereas the mesophilic bacteria concentration was dependent on the inlet concentration. The different behaviors of the two microorganism groups were thought to be due to the different aerodynamic characteristics of the particles that affected the capture by impact in the biofilter bed. The fungus, whose spores had a maximum of diameter size distribution between 2.1 and 3.3 microm, were more effectively captured in the biofilter than the bacteria, which had diameters mainly between 1.1 and 2.1 microm.

The removal of NH3-N from primary treated wastewater in subsurface reed beds using different substrates.

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.