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Sewage sludge composting is a profitable process economically viable and environmentally friendly. In despite of there are several kind of composting types, the use of combined system of semipermeable cover film and aeration air-floor is widely developed at industrial scale. However, the knowledge of the linkages between microbial communities structure, enzyme activities and physico-chemical factors under these conditions it has been poorly explored. Thus, the aim of this study was to investigate the bacterial dynamic and community structure using next generation sequencing coupled to analyses of microbial enzymatic activity and culturable dependent techniques in a full-scale real composting plant. Sewage sludge composting process was conducted using a semi-permeable Gore-tex cover, in combination with an air-insufflation system. The highest values of enzymatic activities such as dehydrogenase, protease and arylsulphatase were detected in the first 5 days of composting; suggesting that during this period of time a greater degrading activity of organic matter took place. Culturable bacteria identified were in agreement with the bacteria found by massive sequencing technologies. The greatest bacterial diversity was detected between days 15 and 30, with Actinomycetales and Bacillales being the predominant orders at the beginning and end of the process. Bacillus was the most representative genus during all the process. A strong correlation between abiotic factors as total organic content and organic matter and enzymatic activities such as dehydrogenase, alkaline phosphatase, and ß-glucosidase activity was found. Bacterial diversity was strongly influenced by the stage of the process, community-structure change was concomitant with a temperature rise, rendering favorable conditions to stimulate microbial activity and facilitate the change in the microbial community linked to the degradation process. Moreover, results obtained confirmed that the use of semipermeable cover in the composting of sewage sludge allow a noticeable reduction in the process-time comparing to conventional open windrows.

Extracellular polymeric substances (EPS) are one of the main components of microbial biofilms, which are markedly influenced by the chemical composition and functional properties of these EPS. This study quantified the adherence capacity of 29 bacterial strains isolated from marine water in Luria–Bertani and Bushnel-Haas culture media. Their capacity to produce EPS and the influence of the culture conditions on the chemical composition and emulsifying activity of their synthesised exopolymers was determined. Eighteen of the bacterial strains in this study produced EPS while eleven were unable to do so. Surface adherence was associated with bacterial growth and with the capacity of the isolates to synthesise EPS. Pseudoalteromonas elyakovii W18 showed the highest values for surface adherence and synthesised a non-bioemulsifier EPS. Principal component analysis (PCA) was used to establish the relationships between the biopolymer characteristics and surface adherence. The efficient adherence of P elyakovii on the surface of K1 (Anoxkaldnes©) carrier was confirming by scanning electronic microscopy.

This study evaluated the composting process of a mixture of sewage sludge and bulking agent in a semi-closed system at industrial scale, which consisted of an aerated static windrow covered with a semi-permeable film. Physical-chemical and respirometric variables were studied and bacteria and fungi were monitored to assess the improvement in the composting process. The system was compared with conventional open windrows in which lengthy composting times are required to obtain stabilized compost, compost sanitation is not always reached and periodical turning must be carried out to avoid anaerobic conditions. The high temperatures reached and maintained during the stage under the semi-permeable film (≈80 °C) permitted the sanitation of the compostable substrate, as demonstrated by the rapid disappearance of Salmonella sp. and the decrease in Escherichia coli in only 5 days of the process. The total microorganism concentration also decreased during the composting process. The rapid decrease in carbon content expressed in volatile solids (VS) (around 41%) showed that the composting process carried out under the semi-permeable film could be shortened to 30 days. The evolution of thermophilic and mesophilic bacteria and fungi was conditioned by the windrow temperature and the biodegradable organic matter content. An adequate linear correlation (r2 = 0.9214) between the total microorganism concentration (log CFU/g) and VS (%) was obtained during the composting process.

In the present study, physico-chemical characteristics, heavy metals content, odour emissions, microbial enumeration and enzymatic activities were analysed during industrial scale composting of sewage sludge partially pre-treated to evaluate the effect of a combined system of semi-permeable film and aeration on these parameters. The results related to physico-chemical parameters showed a decrease in total organic carbon (TOC), organic matter (OM), total carbon (TC) along the process. Volatile solids (VS) were also reduced, reaching 36% at 120 days, which is above the limit according to the current legislation. Similarly, metal content was found to be an important variable in the evolution of enzymatic activity, while lead (Pb), zinc (Zn), and nickel (Ni) were the most influential. Moreover, heavy metals were found below the limit of type B compost quality or European class 2 at the end of the process, which is suitable for agriculture soil. The odorous impact generated during the hydrolytic stage was reduced to an average value of 4 ouE/s. This suggests that, covered stage with the semi-permeable film, could be a viable solution to mitigate odour emissions. The highest temperature was reached at 10 days and it was favoured by semi-permeable film. Temperature promoted the presence of thermophilic bacteria and fungi and indicated an early biodegradation process mediated by microorganisms. Statistical analyses revealed a high correlation of physico-chemical variables with microbial activity. Thus, samples from the first 14 days were highly correlated with enzymatic activities such as β-glucosidase (Ac-βGlu), protease (Ac-Pr), and dehydrogenase (Ac-De), which have usually been involved in the hydrolysis of organic matter.