Behaviour of Main Microbiological Parameters And of Enteric Microorganisms During the Composting of Municipal Solid Wastes and Sewage Sludge in A Semi-Industrial Composting Plant

The Evaluation of Hazards to Man and the Environment during the Composting of Sewage Sludge

Composting is considered an effective treatment option to eliminate or substantially reduce potential hazards relating to the recycling of sewage sludge (SS) on land. The variation of four major types of hazards (heavy metals, instability, pathogenic potential and antibiotic resistance) was studied during laboratory-scale composting of two mixtures of sludge and green waste (1:1 and 1:2 v/v). The heavy metal content of the final compost was governed by the initial contamination of SS, with the bulking agent ratio having practically no effect. The composts would meet the heavy metal standards of the United States of America (USA) and the European Union member states, but would fail the most stringent of them. A higher ratio of bulking agent led to a higher stabilisation rate, nitrogen retention and final degree of stability. A good level of sanitisation was achieved for both mixtures, despite the relatively low temperatures attained in the laboratory system. The antibiotic resistance was limited among the E. coli strains examined, but its occurrence was more frequent among the Enterococcus spp. strains. The type of antibiotics against which resistance was mainly detected indicates that this might not be acquired, thus, not posing a serious epidemiological risk through the land application of the SS derived composts.

Evaluation of laboratory-scale in-vessel co-composting of tobacco and apple waste

Efficient composting process requires set of adequate parameters among which physical-chemical properties of the composting substrate play the key-role. Combining different types of biodegradable solid waste it is possible to obtain a substrate eligible to microorganisms in the composting process. In this work the composting of apple and tobacco solid waste mixture (1:7, dry weight) was explored. The aim of the work was to investigate an efficiency of biodegradation of the given mixture and to characterize incurred raw compost. Composting was conducted in 24 L thermally insulated column reactor at airflow rate of 1.1 L min(-1). During 22 days several parameters were closely monitored: temperature and mass of the substrate, volatile solids content, C/N ratio and pH-value of the mixture and oxygen consumption. The composting of the apple and tobacco waste resulted with high degradation of the volatile solids (53.1%). During the experiment 1.76 kg of oxygen was consumed and the C/N ratio of the product was 11.6. The obtained temperature curve was almost a "mirror image" of the oxygen concentration curve while the peak values of the temperature were occurred 9.5h after the peak oxygen consumption.

Prevalence and survival of potential pathogens in source-segregated green waste compost

Composting of source-separated green waste (SSGW) is essential to meet the EU Landfill Directive target and agricultural land is considered a significant market for the resulting composts. A critical review of the literature was performed to evaluate the potential for pathogens to enter the composting process via SSGW feedstocks and the likelihood of their survival of the composting process and subsequent application to land. This is discussed in the context of application of other organic wastes to land. It was concluded that zoonoses such as verotoxigenic Escherichia coli and Salmonella spp. are unlikely to survive and effective composting process, whereas spore forming organisms are more resistant to composting but are also ubiquitous in the environment. Adherence to existing guidelines, such as those for farm yard manures, is likely to provide a rational degree of health protection for humans and livestock.

Changes in microbial biomass and P fractions in biogenic household waste compost amended with inorganic P fertilizers

The present study was conducted to evaluate the changes in microbial biomass indices (C, N, and especially P) and in P fractions in compost amended with inorganic P fertilizers. In the non-amended control, the average contents of microbial biomass C, N, and P were 1744, 193, and 63 microg g(-1) compost, respectively. On average, 1.3% of total P was stored as microbial biomass P. The addition of KH(2)PO(4) and TSP (triple super phosphate) led to immediate significant increases in microbial biomass C, N, and P. Approximately, 4.6% of the added TSP and 5.8% of the added KH(2)PO(4) were incorporated on average into the microbial biomass throughout the incubation. Approximately, 4.7% of the 1mg and 5.8% of the 2mg addition rate were incorporated on average into the microbial biomass. In the amendment treatments, the average contents of microbial biomass C, N, and P declined by 44%, 64%, and 49%, respectively. Initially, the average size of the P fractions in the non-amended compost increased in the order (% of total P in brackets) resin P (0.7%)<NaOH-extractable P(i) (inorganic P, 3.0%)<NaOH-P(o) (organic P, 6.9%)<NaHCO(3)-P(i) (11.9%)<NaHCO(3)-P(o) (17.0%)<residual P (24.6%)<HCl-P (35.7%). Initially, the relative contributions of the P fractions in the amended compost treatments increased in the order: NaOH-P(i) (1.0%)<resin P (2.5%)<NaOH-P(o) (4.5%)<NaHCO(3)-P(o) (4.9%)<residual P (14.8%)<HCl-P (15.2%)<NaHCO(3)-P(i) (57.1%). At the end of the 56-day incubation, the largest and highly soluble fraction of NaHCO(3)-extractable P(i) had decreased in place of the less soluble fractions NaOH-extractable P(i) and P(o), but especially HCl-P, but not in place of the insoluble fraction of residual P. The microbial biomass is able to rapidly store significant amounts of easily soluble P and to prevent it from adsorption or other fixation processes.