Characterisation and perspectives of energetic use of dissolved gas recovered from anaerobic effluent with membrane contactor.

Biogas is a source of renewable energy, and its production and use has been validated in anaerobic-based sewage treatment plants (STPs). However, in these systems, a large amount of methane is lost as dissolved methane (D-CH4) in the liquid effluent. In this study, the characteristics and potential energetic uses of the gas recovered during the desorption of D-CH4 from anaerobic effluents with hollow fibre membrane contactors were investigated. A pilot-scale experiment was performed using sewage and two types of membrane contactors. The recovered gas contained considerable amounts of CH4, CO2, H2S, N2, and O2; therefore, a gas upgrade is required prior to its use as a biofuel. The recovery process should be energetically self-sustainable, and induce a considerable decrease in the STP carbon footprint. Recovering D-CH4 with membrane contactors could increase the energetic potential of anaerobic-based STPs up to 50 % and allow for more sustainable systems.

Persistence of pathogens and bacterial community dynamics in tropical soil after application of raw sewage.

The objective of this work was to evaluate the persistence of faecal indicators and pathogenic organisms (Salmonella spp., Escherichia coli and viable helminth eggs) and the structure/diversity of bacterial communities in soil receiving raw sewage (RS) for an extended period of application (3 uninterrupted years). In the experimental design, three treatments were defined: (1) Control soil, characterized by the analysis of a composite sample collected in an area of similar soil, but not a recipient of RS (TSC); (2) Soil receiving conventional mineral fertilization, and furrow irrigation with supply water (TW); and (3) Fertirrigated soil with RS applied by furrows (TF). The results of persistence of pathogenic organisms and indicators in TF indicated a sanitary quality similar to the control soil (TSC), thus potentially bringing low risks of contamination with pathogens present in the soil. The presence of viable helminth eggs was not identified in any treatment studied, because of its low concentration in the raw sewage of the studied system. The TW, TF and TSC treatments had 34.8% of bacterial diversity in common. The bacterial composition of the soil showed a predominance of the Proteobacteria phylum in all treatments studied; however, TF was the one with the highest relative abundance of this phylum (44.8%).

Macronutrient distribution in soil subjected to raw sanitary sewage application by closed-end furrows.

This work aimed to evsaluate the influence of raw sanitary sewage (RS) application in closed-end and level-bottom furrows on the distribution of macronutrients and sodium in the soil along its depth. The applied amount of RS was controlled due to the harmful effect of sodium, with a weekly application over three consecutive years. The experimental design consisted of two experimental plots receiving RS, one with alternating the site of effluent application (alternation of inlet and outlet-TFA) and the other without alternating the site of application (only inlet-TFN); and two experimental plots receiving conventional mineral fertilization, both irrigated with public water supply, where one alternated the site of water application (alternation of inlet and outlet-TWA) and the other without alternating the site of application (only inlet-TWN). The inversion of the flow direction with RS application in the closed-end furrows (TFA) provided a better distribution of nutrients in the soil along its length. There was no significant difference in the levels of macronutrients and sodium between the initial and final regions of the furrow soil. In contrast, the fixed flow direction experimental unit (TFN) exhibit a significant difference between the initial and final levels of total nitrogen, phosphorus, potassium and sodium in the closed furrows with mean concentrations of 265.2, 16.2, 46.7 and 110.0 mg dm-3, respectively.