Microbial, chemical, and isotopic monitoring integrated approach to assess potential leachate contamination of groundwater in a karstic aquifer (Apulia, Italy).

Landfill sites are subjected to long-term risks of accidental spill of leachate through the soil and consequential contamination of the groundwater. Wide areas surrounding the landfill can seriously be threatened with possible consequences to human health and the environment. Given the potential impact of different coexisting anthropic pollution sources (i.e., agriculture and cattle farming) on the same site, the perturbation of the groundwater quality may be due to multiple factors. Therefore, it is a challenging issue to correctly establish the pollution source of an aquifer where the landfill is not isolated from other anthropic land uses, especially in the case of a karstic coastal aquifer. The present study is aimed at setting in place an integrated environmental monitoring system that included microbiological, chemical, and isotope methods to evaluate potential groundwater pollution in a landfill district in the south of Italy located in Murgia karstic aquifer. Conventional (microbial plate count and physical-chemical analyses) and advanced methods (PCR-ARISA, isotope analysis of δ18O, δ2H, 3H, δ 13C, δ 15N-NO3-, and δ 18O-NO3-) were included in the study. Through data integration, it was possible to reconstruct a scenario in which agriculture and other human activities along with seawater intrusion in the karst aquifer were the main drivers of groundwater pollution at the monitored site. The microbiological, chemical, and isotope results confirmed the absence of leachate effects on groundwater quality, showing the decisive role of fertilizers as potential nitrate sources. The next goal will be to extend long-term integrated monitoring to other landfill districts, with different geological and hydrogeological characteristics and including different sources of pollution, to support the ecological restoration of landfills.

The effect of substituting energy crop with agricultural waste on the dynamics of bacterial communities in a two-stage anaerobic digester.

The replacement of energy crops with agricultural waste in biogas production through anaerobic digestion (AD) is both an environmentally sustainable and economically profitable strategy. However, the change of feeding mix in AD might result in nutrient imbalance or increase of the ammonium concentration, negatively affecting the activity of the microbes responsible for the process. In the present study the structure and dynamics of the bacterial communities of a full-scale two-stage AD plant, composed of a hydrolysis/acidogenesis (H) and an acetogenesis/methanogenesis (M) tanks, was monitored during feedstock substitution. Energy crop (triticale) was replaced by poultry manure litter and olive mill pomace. The increase percentage of poultry manure litter (up to 8.6%) and olive mill pomace (up to 30.5%) in the recipe incremented the total solids (up to 21% in H) and, consequently, the nitrogen content in the digestate (6.7 g N/kg in the solid fraction in H and 4-5 g NH4+-N/L in the liquid fraction). This favored the growth of Lactococcus sp. with consequent increment of lactate production (∼ 1 mg L-1 last two days of the survey) and the establishment of Weissella and Lactobacillus spp. Syntrophic acetate-oxidizers, including Syntrophaceticus (6% ± 1.7%), were detected manly in M but were negatively affected by the addition of the poultry manure litter, while the sulfate-reducing bacteria correlated with the variations of the volatile fatty acids. Planctomycetes putatively capable of anammox process were also found in the H during the first two days of the survey and accounted for 0.3 ± 0.01% of the total bacterial community. The stability of the process during feedstock change is the result of the shift of bacterial populations of different functional groups that showed peculiar adaptation patterns in the two stages of the plant.