Environmental implications of combustion of rice husk at high temperatures and for an extended period for energy generation.

The most common alternative for the management and valorization of rice processing waste is the combustion of rice husk (RH) for energy generation. The environmental risk assessment of the ash generated during the combustion of the RH to obtain energy has remained understudied. Disposal of rice husk ash (RHA) on agricultural land is the most common outcome, which could pose a risk to both natural ecosystems and human health. The objective of this study was to characterize the physicochemical composition and the phytotoxicity, cytotoxicity, and genotoxicity of RHA obtained from three distinct combustion processes. The evaluation processes were 800-900 °C in up to 5 min (I), 800-900 °C in 15-20 min (II), and 600-700 °C in 15-20 min (III). Furthermore, the content, pH, and concentrations of Al, Cd, Cu, Fe, Mg, Mn, Mo, Na, Ni, and Ti present in the ashes were determined. The germination index for two vegetable seeds was subsequently evaluated. By measuring the mitotic index and frequency of chromosomal aberrations, the cytotoxicity and genotoxicity were determined. It was observed that RHA produced by combustion of RH at higher combustion temperatures for an extended period exhibited different physicochemical properties, in addition to higher levels of phytotoxicity, cytotoxicity, and genotoxicity.

Start-up phase optimization of two-phase anaerobic digestion of food waste: Effects of organic loading rate and hydraulic retention time.

The effects of organic loading rate (OLR) and hydraulic retention time (HRT) on the dynamics of acidogenic and methanogenic processes in two-phase anaerobic digestion (TPAD) of food waste (FW) were investigated to determine the start-up operational conditions. Seven arrangements of TPAD systems under mesophilic conditions were evaluated, each containing one acidogenic reactor and one methanogenic reactor. The work analyzed two HRTs (2 and 3 days) and four OLRs (2, 3, 4 and 5 kgVS.m-3.d-1). The 2D5KG system obtained VS and COD removal of 68% and 72%; SMP of 273 Lmethane.kg.VS-1. The 3D4KG system obtained VS and COD removal of 70 and 66%; SMP of 252 Lmethane.kg.VS-1. Valeric acid predominated in the acidogenic reactor in both HRT and OLR evaluated, followed by butyric acid. In the methanogenic reactor, the main methane production route was the butyric acid conversion into acetic acid and finally methane. Higher OLR benefits the methane production. The microbiological profile indicated the pathway of methanogenesis by acetoclastic methanogenesis. The canonical correlation analysis allowed to verify that the groups are independent and, therefore, the variables analyzed in the acidogenic reactor have an influence on the methanogenic reactor.

Physical-chemical pre-treatment of sanitary landfill raw leachate by direct ascending filtration.

Several environmental problems in Brazil are caused by the accelerated urban and industrial growth and by the multiplicity of urban waste generated. Waste disposal in landfills is still common practice in Brazil. This work was conducted in sand filters and activated carbon column, proposing an alternative for the physical-chemical treatment of leachate as a pre-treatment to preserve the biological process. The results showed reductions of up to 74% for COD, 47% for BOD5, 93% for color, 90% for ammonia and an increase from 0.3 to 0.9 in the BOD5/COD ratio. Although the results obtained do not fall within the limits of the legislation, the results for ammonia concentration was reduced by 33.25% and 85.37% after filtration and activated carbon column treatment respectively. The use of activated carbon columns resulted in an excellent performance in the reduction of heavy metals in the leachate. The performance demonstrated a removal of 60-96%. Limitations were found in the length of the filtration races, as a limiting factor in the process. The results show the potential of using direct upward filtration with sand and activated carbon filters for the treatment of landfill leachate.

Ammonia recovery from air stripping process applied to landfill leachate treatment.

The leachate is a type of effluent from landfills containing high concentrations of ammonia, even after normal treatment procedures are applied. Due to its characteristic, the leachate can adversely impact the environment and public health. Leachate treatment seeks to remove a series of compounds with adverse characteristics present in this type of effluent. Ammonia nitrogen is the main problem, easily observed in concentrations near 2000 mg/L. The effluents with high concentrations of ammonia nitrogen can stimulate the growth of algae, reduce the dissolved oxygen in rivers, and cause toxicity on the aquatic biota, even in low concentrations. Many research for treatment methods aiming to remove this compound, specifically, have been increasingly deeper, mainly by physical-chemical processes. This study aimed to test the process of air stripping in a closed system and pilot scale, applied on leachate treatment of landfills, to remove the high concentrations of ammonia nitrogen and its recovery by the chemical absorption of ammonia on phosphoric acid, resulting in a product with potential application as agricultural fertilizer, the ammonia phosphate. The leachate flows used were 9, 18, 20, and 40 L/h, and the air flows were 1800 and 3600 L/h. Calcium carbonate (standard grade), commercial hydrated lime (CHL), and sodium hydroxide (standard grade) were used for pH adjustments. To the ammonia recovery, three flasks were used with 2.5 L of a phosphoric acid solution of 0.12 and 0.24 mol/L. The air stripping tower removed an average of 98% of ammoniacal nitrogen, with an operating time of 4 to 9 days. The volume of air consumed to remove 1 g of ammoniacal nitrogen varied from 9, 91, and 21.6 m3. The ammonia recovery was about 92% using a phosphoric acid solution, producing the ammonia phosphate.

The analysis of green roof's runoff volumes and its water quality in an experimental study in Porto Alegre, Southern Brazil.

The green roofs are structures characterized by the application of vegetation cover in the buildings, using adequate waterproofing and drainage systems. It allows the reduction of surface runoff and delay in peak flow, contributing to the mitigation of flood events in urban areas. Therefore, this study aimed to evaluate the effect of the use of vegetal coverings on the surface runoff, taking into account quantitative and qualitative aspects, using an experimental module installed in the city of Porto Alegre, Brazil. The experimental station consisted of four modules: two horizontal modules with and without vegetation cover and two modules with slopes of 15° with and without vegetation cover. It was evaluated 19 precipitation events, and it was verified the volumes drained in each module after 3, 6 and 12 h from the beginning of precipitation. The water samples were collected in order to analyse the quality of the runoff from the experimental modules. The results have shown that the use of vegetal coverings can provide better distribution of the surface runoff, as well as a decrease of the speed of excess water release with no surface runoff in the first 3 h after the onset of rainfall in the horizontal module. Additionally, it was proved the reduction in drained volumes, with the flat module with vegetation cover being capable of retaining completely precipitations with volumes of approximately 22 mm. The vegetation cover module in roofs was the one that has presented better results regarding the reduction of the flow, presenting an average retention percentage of 91.7% for the first 3 h, indicating that the slope is an important factor. The physical-chemical analysis of the water shows that for all analysed modules, it is possible to use water for non-potable uses, although the water quality of the modules with vegetation cover is lower when compared to the water coming from the module without vegetation cover.