Stabilized Sewage Sludge Research Articles

Sewage Sludge as a Tool in Limiting the Content of Trace Elements in Avena sativa L. on the Soil Polluted with Diesel Oil.

The aim of the research was to determine the effect of soil contamination with diesel oil (0; 5; 10 and 15 cm3 kg−1 of soil) on the content of trace elements in the aboveground parts of oat (Avena sativa L.). Stabilised sewage sludge was used to mitigate the likely negative impact of diesel oil on the plant. Growing soil contamination with diesel oil had a significant impact on the content of trace elements in the aboveground biomass of oat. In the series without sewage sludge, the contents of the analysed elements, except for chromium, zinc, copper and cobalt, were positively correlated with the increasing doses of diesel oil. The largest increase in the content was recorded in the case of manganese. The sewage sludge used to reduce the influence of diesel oil on the chemical composition of oat had a positive effect on the content of the analysed trace elements. Compared to the series without the addition of a stabilised sewage sludge, it contributed to a reduction in the average content of chromium, nickel, copper, manganese and cobalt in the aboveground parts of oat plants. No significant effect of the applied remediation treatment was noted for cadmium, and the results were equivocal for iron.

Geotechnical Applications of Sewage Sludge Stabilized with Biomass Ash and its Effect on Soil Nutriential Properties: A Critical Review

In this review article the usage of waste sewage sludge and the biomass ash for improving the engineering and non-engineering properties’ of both concrete and soil are discussed in detail. Numerous past research works were studied in detail so as to predict the behavior of biomass ash and waste sewage sludge when used for the stabilization process of soil and concrete. Past studies related to the usage of stabilized sewage sludge and biomass ash were studied in a detailed manner and depending upon the past studies several conclusions has been drawn which are discussed further. Several studies related to the usage of the waste sewage sludge for improving soil physical, chemical and biological properties showed that the usage of waste sewage sludge improve the physical properties, chemical properties, macro-nutriential properties and micro-nutriential properties up to a great extent. Depending upon the results of the past studies it can be concluded that the usage of sewage sludge has positive impact over all the properties of soil and this waste should be utilized in improving the properties of soil rather than dumping. Numerous studies related to the usage of the biomass ash showed that biomass ash has positive impact over both soil as well as concrete. Studies related to the usage of the biomass ash in soil showed that there was a positive response of the stabilized soil after its stabilization with the biomass ash. Studies related to the usage of the biomass ash in concrete showed that the biomass ash can be used up to 10 percent replacement of the ordinary Portland cement so as to attain maximum strength results from it.

The Efficiency of the Biogas Plant Operation Depending on the Substrate Used

The study aimed to assess the most efficient solution of raw material management in selected biogas plants into the concept of circular economy and evaluate the most efficient solution of raw material management in selected biogas plants due to the quality and quantity of the feed and the final product obtained, which is biogas, as well at the closed circulation (circular economy). The study evaluated two agricultural biogas plants on a real scale and one at the sewage treatment plant (in real scale) in northeastern Poland. A year-long study showed that in technical terms, the best work efficiency is achieved by agricultural biogas plants processing: silage, manure, apple pomace, potato pulp (biogas plant No. 1), followed by biogas plant No. 3 processing chicken manure, decoction, cattle manure, poultry slaughterhouse waste (sewage sludge, flotate, feathers), and finally, the lowest efficiency biogas plant was No. 2, the sewage treatment plant, which stabilized sewage sludge in the methane fermentation process. Moreover, based on the results, it was found that agricultural biogas gives the best efficiency in energy production from 1 ton of feed.

Extent of bioleaching and bioavailability reduction of potentially toxic heavy metals from sewage sludge through pH-controlled fermentation

Utilization of anaerobically stabilized sewage sludge on arable lands serve as a renewable alternative to chemical fertilizers as it enables recycling of valuable nutrients to food chain. However, probable presence of heavy metals in sewage sludge restricts the use of stabilized sludge on lands. In this study, a novel approach based on pH-controlled fermentation and anaerobic metal bioleaching was developed to reduce ecotoxicity potential of fermented sludge prior to its land application. Sewage sludge was subjected to pH-controlled fermentation process at acidic, neutral, and alkaline pH levels with the aim of increasing metal solubilization and decreasing bioavailable metal fractions through anaerobic bioleaching. Alkaline reactor performed the best among all reactors and resulted in 3-fold higher hydrolysis (34%) and 6-fold higher acidification (19%) efficiencies along with 43-fold (in average) higher metal solubilization than that of neutral pH reactor. As a result of alkaline fermentation, 32–57% of the metals remained as bioavailable and 34–59% of the metals were encapsulated as non-bioavailable within solid fraction of fermented sludge (biosolid), whereas 8–12% of total metal was solubilized into fermentation liquor. Our results reveal that anaerobic bioleaching through alkaline fermentation enables biosolid production with less metal content and low bioavailability, facilitating its utilization for agricultural purposes.

Removal and recovery of heavy metals from sewage sludge via three-stage integrated process

Heavy metal contamination of sewage sludge is one of the concerns preventing its land application. Traditional processes applied for stabilization of sewage sludge are still inadequate to serve sustainable solutions to heavy metal problem. In this study, fermentation and bioleaching potentials of sewage sludge were investigated in anaerobic reactors for either non-pretreated or ultrasonicated sludge at three different pH regimes (free of pH regulation, acidic, and alkaline). The results of the study revealed that combination of ultrasonication pretreatment and alkaline fermentation performed the best among the other cases, resulting in 33.7% hydrolysis, 10.5% acidification, 11–33% metal leaching, and up to 25% reduction in bioavailability of potentially toxic heavy metals. Bioleaching effluent obtained from the best performing reactor was subjected to membrane-based metal recovery. A supported liquid membrane impregnated with a basic carrier successfully recovered soluble metals from the bioleaching effluent with an efficiency of 39–68%. This study reveals that the proposed three-stage process, ultrasonication pretreatment-alkaline fermentation-supported liquid membrane, effectively produces stable sludge with reduced heavy metal toxicity and recovers metals from organic waste streams.

Enhanced heavy metal leaching from sewage sludge through anaerobic fermentation and air-assisted ultrasonication

Interest in using stabilized sewage sludge in agriculture is mainly to benefit from its nutrient content, soil conditioning properties, and water holding capacity. Therefore, sludge management practice needs to be directed from treatment liability towards the recovery of chemical assets embedded in sludge. In this study, anaerobic fermentation process integrated with a new treatment method; i.e., air-assisted ultrasonication, was used to assess the leaching of heavy metals (HM) from waste activated sludge (WAS). Fermentation processes resulted in 9390 mg COD/L of volatile fatty acids (VFAs) production, 26% Ni solubilization and up to 3.4% solubilization of other target metals (Cu and Zn). Application of the air-assisted ultrasonication as a post-treatment to fermentation process stimulated the migration and transformation of HMs to the liquid fraction of the digestate. Applying specific energy input greater than 9 kJ/g total solids (TS) through ultrasonication and supplying air with constant flow rate of 0.875 L of air/(L of digestate.min) resulted in leaching of more than 83% of Ni, 82% of Cu and 80% of Zn.

Impact of Aerobic Stabilization of Sewage Sludge on PAHs Concentration in Reject Waters

Impact of Aerobic Stabilization of Sewage Sludge on PAHs Concentration in Reject Waters

Effect of hydrodynamic cavitation on flocs structure in sewage sludge to increase stabilization for efficient and safe reuse in agriculture

Sewage sludge is the by-product of wastewater treatment processes. Its reuse is central to a circular economy approach and offers a sustainable alternative to its disposal. Treated sludge contains a wide range of nutrients (mainly nitrogen, phosphorus, and potassium), which favor its sustainable employment for agricultural purposes (land-spreading, compost production) and environmental requalification interventions (forestry, silviculture, land reclamation and revegetation). However, if not properly treated, sewage sludge can contain various contaminants such as heavy metals, organic pollutants, pathogens, and other emerging contaminants, which pose a threat for crops production and human health. Hydrodynamic cavitation (HC) is an eco-friendly and cost-efficient pretreatment that can enhance sewage sludge stabilization in both anaerobic and aerobic digestion units, thereby making safe its management and disposal. In this study, HC was used for the gradual disintegration of activated sludge (reaching a maximum disintegration degree (DDPCOD) of 19.2% after 8 h of treatment), and the solubilization of the dissolved organic matter (increasing the Soluble Chemical Oxygen Demand (SCOD) from 244 to 4,578 mg L−1 after 8 h of treatment). Then, both dynamic light scattering analysis and stereoscopic microscope observations proved that HC can also lead to a size reduction of sludge suspended particles. In addition to evaluate the HC treatment efficiency, in this work was also provided a brief discussion on the possible procedures to be followed for the safe and efficient sewage sludge disposal on land after it has been HC-treated.

Role of organic amendment application on soil quality, functionality and greenhouse emission in a limestone quarry from semiarid ecosystems

One strategy for restoring degraded soils by opencast mining in semiarid regions is the application of organic amendments. However, selecting an appropriate organic amendment that improves soil quality and functionality for recovery in the short-term without a high contribution to increased CO₂ emissions is important for improving restoration strategies. Therefore, the objective of this work was to study the short and medium-term changes in physico-chemical and biological properties in restored soils with organic amendments from a limestone quarry (SE, Spain). Several restoration treatments were applied consisting stabilized sewage sludge, vegetable compost garden waste, vegetable compost from greenhouse crop residues and two mixtures thereof, then native plants were planted. After six months several soil properties were evaluated (electrical conductivity (EC), pH, total organic carbon (TOC), total nitrogen (TN), assimilable phosphorus (AP), soil water retention, carbohydrates and polyphenols content, enzymatic activities, bacteria and fungi fatty acids and soil respiration). Some physico-chemical soil properties and the survival rates and biovolume of the introduced native plants, as well as the percentage of land cover occupied by wild plants, were also analyzed 2 years after the application of the amendments. Organic amendments improved significantly all soil properties compared with unamended soils. Labile organic matter forms (carbohydrates and polyphenols) showed significant positive correlations with parameters related to microbial activity. Restored soils with sewage sludge had the highest significant labile C values, following by its mixtures. All organic amendments increased in situ CO₂ release, a positive priming effect and organic matter mineralization, being these properties higher in sludge-treated soils than in the rest restored and non-amendment soils. The content of TOC and TN and water retention remained similar two after the application of the amendments, but the EC decreased in restored soils. Nevertheless, despite PCA analysis clearly demonstrated that all restoration treatments had an important effect on the functionality and soil quality, vegetable compost from garden waste or from horticultural greenhouse crop waste amendments were the best restoration treatments for short and medium-term restoration of degraded quarry soils in harsh environmental and climate conditions because they also presented lower CO2 emission rates to the atmosphere and the highest survival and growth rates of the introduced plants and wild cover in the experimental plots.

Bioavailability and eco-toxicity of heavy metals in chars produced from municipal sewage sludge decreased during pyrolysis and hydrothermal carbonization

The rapid increase in municipal sewage sludge production due to quick urbanization and economic development raised significant socio-economic and environmental issues in recent years. Although the increase in heavy metals' (HMs) immobilization through pyrolysis and hydrothermal carbonization (HTC) of municipal sewage sludge are reported in previous investigations, but there is still limited information available regarding the potential environmental risks associated with these processes. This study investigated the chemical speciation, bioavailability and eco-toxicity of HMs (Zn, Cu, Ni and Pb) in biochars (pyrolysis temperatures of 450 °C and 600 °C) and hydrochars (HTC temperature of 180 °C) produced from two sludge feedstocks (sludge cake and stabilized sewage sludge). The HTC generally resulted in higher char yield compared to pyrolysis process. The raw sewage samples showed a flat morphological surface texture, while HTC process increased the porosity and surface area of produced hydrochars. The pyrolysis process also increased the porous structures and surface morphology of biochars, with higher porosity in biochars produced at 600 °C. The pH value of hydrochars was significantly (P < 0.05) lower than the sludge feedstock, while pyrolysis process significantly (P < 0.05) increased the pH value of produced biochars. The H/C and O/C ratios of char products were gradually decreased by increasing production temperature, illustrating the formation of higher aromaticity and stronger carbonization. The concentration order of HMs in sludge feedstock was Zn > Cu > Pb > Ni, and with thermochemical processes the concentration of HMs increased in biochar and hydrochar products. The enrichment of HMs in all biochars was significantly (P < 0.05) higher than hydrochars. The concentration of HMs significantly (P < 0.05) reduced in bioavailable fraction and increased in stable fraction during pyrolysis and HTC processes. Consequently, the potential environmental risk and eco-toxicity of HMs significantly (P < 0.05) decreased in hydrochars and biochars with low or no environmental risk of direct land application.

Effects of Sewage Sludge Stabilization Processes on Soil Fertility, Mineral Composition, and Grain Yield of Maize in Successive Cropping

The final disposal of sewage sludge (SS) in agricultural areas is considered economically and environmentally viable, but few studies on the effects of sludge stabilization processes on SS fertilizing potential are available. The present study evaluated two forms of SS stabilization on the shoot biomass, yield, and concentration of nutrients in the soil and plants in three successive maize croppings. The raw sludge was chemically stabilized (CSS) and composted (TSS) through the addition of calcium oxide and co-composting with plant residues, respectively. Five rates of each type of SS (0, 10, 20, 30, and 40 t ha−1 dry weight) were applied to the soil in a family farm of NE Brazil. A mineral fertilization treatment was used to assess the SS fertilizer potential. Changes in soil chemical characteristics (pH, organic matter, and nutrient available contents), plant mineral composition, and maize biomass and yield were assessed at each crop cultivation. Applying sewage sludge to the soil elevated the soil organic matter and the availability of N, P, Fe, Mn, Zn, and Cu, reflecting in higher accumulation of these nutrients by plants. The CSS was more efficient in increasing soil pH than SS composting. In the first harvest, maize yield in CSS was 34% higher than that obtained with mineral fertilization. The two types of sludges had different effects on soil characteristics, plant mineral composition, and maize yield. The CSS residual effect on soil pH can dismiss soil liming. Composted sludge maintained higher soil organic matter levels in the soil with the successive croppings and promoted higher soil N concentrations in the first two croppings. Both sludges increased and maintained adequate available P concentrations in the soil throughout the successive crops. The results support SS’s efficiency in providing nutrients to plants, improving soil properties, and boosting crop productivity in low-input agriculture systems.

Stabilized sewage sludge: Sanitary aspects and potential for conversion to biosolids

The improvement of wastewater treatment techniques is of crucial importance for effluent quality, but it also results in an increased amount of waste sludge. Dehydrated sludge contains organic matter and nutrients, and therefore it can be used in agriculture and bioremediation, but it is considered a potential source of environmental pollution. As the sludge analyzed in the research does not contain impermissible levels of organic and inorganic pollutants, the aim of the research was to examine microbiological, particularly sanitary, aspects and potential for its further use. Microbial diversity was determined by the standard serial dilution technique and selective media, and sanitary quality indicators (total coliforms, fecal coliforms, Escherichia coli and Salmonella spp.) were determined by the MPN method. The abundance of fungi, actinomycetes, and bacteria (ammonifiers, spore-forming bacteria and Pseudomonas spp.) indicate possibilities for further use of the sludge. The chemical analysis included the following parameters: total nitrogen (N), phosphorus in the form of P2O5 (available P), organic carbon (C), C/N ratio, pH, and water content. The chemical composition indicates the potential of sewage sludge to be used as a soil fertilizer, but its C/N ratio is not adequate to enable successful conversion to biosolids by the composting process. The obtained results indicate a significant level of microbiological contamination, which was most pronounced in the centre of the stabilized sludge pile. The research showed the necessity to conduct further studies on the microbial diversity and sanitary aspects of sewage sludge for proper waste sludge management.

Controlled-Release Fertilizer and Container Volume to Produce Inga laurina Seedlings

This study evaluated the production of Inga laurina (Sw.) Willd seedlings in 110 and 280 cm3 tube containers and growing doses (0, 3, 6 and 12 kg m-3) of controlled-release fertilizer (CRF) (15-09-12) and their performance at 5 and 12 months after outplanting. The experiment was conducted using a randomized split-plot design, in a 2 x 4 arrangement (tube volumes x CRF doses). Stabilized sewage sludge from urban origin was used as substrate. It was assessed growth and biomass of the seedlings in nursery, as well as survival and growth after outplanting. Containers of 280 cm3 and doses between 6 to 12 kg m-3 produced seedlings in less time, with higher growth and biomass. At 12 months after outplanting, seedlings presented acceptable growth and mortality rate with doses equal or greater than 6 and 3 kg m-3 of CRF, respectively, for the 110 and 280 cm3 tube.

Effect of pyrolysis temperature on removal of organic pollutants present in anaerobically stabilized sewage sludge

Sewage sludge was excluded from the list of component materials for the production of EU fertilizing products and it was banned as feedstock to produce pyrolysis & gasification materials in European Commission’s technical proposals for selected new fertilizing materials under the Regulation 2019/1009 (STRUBIAS report). This exclusion of pyrolysis as a viable way to treat sewage sludge was mainly due to the lack of data on the fate of organic pollutants at pyrolysis conditions. In this work, we are addressing this knowledge gap. We studied slow pyrolysis as a potential process to efficiently treat organic pollutants present in stabilized sewage sludge. Sewage sludge was pyrolyzed in a quartz fixed bed reactor at temperatures of 400–800 °C for 2 h and the sludge and resulting sludge-chars were analyzed for the presence of four groups of organic pollutants, namely (i) polychlorinated biphenyls (PCBs), (ii) polycyclic aromatic hydrocarbons (PAHs), (iii) pharmaceuticals, and (iv) endocrine-disrupting and hormonal compounds. Pyrolysis at ≥ 400 °C effectively removed pharmaceuticals (group iii) to below detection limits, whereas pyrolysis at temperatures higher than 600 °C was required to remove more than 99.8% of the compounds from groups i, ii and iv. Based on these findings, we propose, that high temperature (>600 °C) slow pyrolysis can satisfactory remove organic pollutants from the resulting sludge-char, which could be safely applied as soil improver.

Effects of Mesophilic Anaerobic Digestion and Thermophilic Anaerobic Digestion on the Risk and Stability of Heavy Metals in Sludge

Anaerobic digestion is widely used for sewage sludge stabilization. Different anaerobic digestion methods have different impacts on the speciation and stability of heavy metals in sludge. This study investigated the response of the speciation and stability of heavy metals in sludge to the treatment of mesophilic anaerobic digestion-mechanical dewatering and thermal hydrolysis pre-treatment-thermophilic anaerobic digestion. The results showed that the process of mesophilic anaerobic digestion increased the contents of Cd, Cr, Cu, Ni, and Zn in the sludge, increasing its contamination level and potential ecological risks. In contrast, the thermophilic anaerobic digestion process increased the contents of Cd, Cr, and Pb in the sludge, reducing the level of heavy metal contamination and potential ecological risks. It was found that the main contaminated metals were Cd and Zn in Plant N and Cd in Plant S. Cd has the highest risk factor and is the highest risk contributor to the potential ecological risk of all the types of sludge. The sum of reducible and the exchangeable fractions of Cd, Ni, Pb, and Zn reduced, and the residual fraction of Cd, Cr, Cu, and Ni decreased after mesophilic anaerobic digestion. This indicated that the process of mesophilic anaerobic digestion changed the proportion of potential toxicity and steady state of the heavy metals into direct toxicity. After thermophilic anaerobic digestion, the exchangeable proportion of Cd, Cr, Cu, Pb, and Zn decreased, and the steady state of Cd, Cr, Cu, Ni, Pb, and Zn decreased. After the thermophilic anaerobic digestion process, the proportions of bio-availability and mobility of heavy metals therefore decreased, and the proportions of steady state also reduced. The potential toxicity increased.

Technological characteristics of reject waters from aerobic sludge stabilization in small and medium-sized wastewater treatment plants with biological nutrient removal

Most studies on the impact of reject waters recycled from sludge processing in the multi-phase activated sludge process focus on anaerobic sludge treatment in large wastewater treatment plants, leaving apart the processes of aerobic sludge stabilization often used in smaller facilities in rural and suburban areas. The article presents the results of tests carried out in three small and medium-sized wastewater treatment plants with biological removal of biogenic compounds that use aerobic stabilization to process sludge. The research concerned the quantity and quality of reject waters generated in the process of aerobic stabilization and dewatering of sewage sludge and their impact on the multi-phase activated sludge process. The results showed that the average volume of generated reject waters ranged from 3.2 to 5% of the incoming wastewater volume. The average share of organic compounds and total nitrogen loads contained in reject waters did not usually exceed 5–10% of the loads in raw wastewater but reached almost 50% in the case of total phosphorus. Studies indicated that the composition of the supernatant from aerobic stabilization is strongly dependent on the course of the process. The best quality was obtained for cyclic operation of the aerobic stabilization tank with 16 h of aeration and 8 h of settling. The results also showed the negative impact of sudden discharges of reject waters from sludge processing to a multi-phase biological reactor, which can be reduced by using an appropriate equalization tank and pretreatment of the side stream to reduce the recirculation of phosphorus.

Use of a stabilized sewage sludge in combination with gypsum to improve saline-sodic soil properties leached by recycled wastewater under freeze-thaw conditions

Soil salinization is a major environmental hazard that limits agricultural production. Using sewage sludge and recycled wastewaters in amelioration of saline-sodic soils is one of the most effective ways to dispose waste. However, a very low initial permeability of soil in the freeze-thaw conditions can make improvement difficult. Therefore, column experiments at a soil depth of 15 cm have been conducted to determine the effects of the combination of four stabilized sewage sludge doses (0, 50, 100, 150 t ha−1), three freeze-thaw cycles (0, 5, 10 times) and two water types (FW: freshwater, RWW: recycled wastewater) on gypsum-treated saline-sodic soil properties. The effects of non-saline-sodic RWW on the soil properties were similar to the FW in total 22.5 cm leaching amount. Compared to gypsum alone and initial values, sewage sludge increased wet aggregate stability, organic matter, total N and exchangeable Ca + Mg while it decreased pH, exchangeable Na and CaCO3. Saturated hydraulic conductivity was not induced by sewage sludge although exchangeable sodium percentage and electrical conductivity were reduced by 44% and 63.6%, respectively. Negative effects of freeze-thaws on hydraulic conductivity and salinity and sodicity elimination were not observed, while pH and aggregate stability were negatively affected from ten freeze-thaws. Overall, it can be concluded that the improvement of hydraulic conductivity is attributed to the further improvement of soil structure from more strong wet aggregate stability via additional sewage sludge and leaching amounts.

Detailed Analysis of Sewage Sludge Pyrolysis Gas: Effect of Pyrolysis Temperature

Conventional methods of sewage sludge disposal are often limited by their environmental impact and economic demands. Pyrolysis has been studied as a viable method for sewage sludge disposal and transformation into usable products. Pyrolytic products may have various uses, and their complex characteristics shall be described to assess their potential for safe utilization. Here, we studied slow pyrolysis of stabilized sewage sludge in a fixed bed reactor at 400–800 °C to describe the composition of the pyrolysis gas and the condensate fraction. We found that condensate elemental composition was practically independent of pyrolysis temperature. On the other hand, the composition of the pyrolysis gas was strongly temperature-dependent regarding both the share of major components (H2, CO, CO2, CH4) and C2–C6 hydrocarbons speciation (which as a sum attributed to 7–9 vol. % of the gas). The increase in pyrolysis temperature also resulted in increasing the N2 content of the gas, whereas the sulfur containing gas compounds were substantially diluted in the increasing gas volume.

Alkalinized sewage sludge affects nutrition and growth of common bean cultivated in Ferralsols

A aplicação de lodo de esgoto alcalino em solos agrícolas aumentou, mas as implicações nutricionais para as culturas ainda são pouco exploradas. Com o objetivo de avaliar o efeito do lodo de esgoto alcalinizado na nutrição e crescimento do feijoeiro (Phaseolus vulgaris L.), foi realizado experimento em casa de vegetação com três Latossolos e três tipos de lodo de esgoto. Amostras de Latossolos (texturas franca, muito argilosa e argilosa) foram coletadas em três regiões geologicamente distintas do estado do Paraná, Brasil: arenito, basalto e argilito. Amostras de lodo de esgoto foram estabilizadas com calcário e posteriormente misturadas com as amostras de solo. Lodo de esgoto alcalinizado e calcário foram aplicados aos solos nas taxas correspondentes a 50, 100, 150 e 200% da quantidade necessária para o solo atingir pH 5,5. Aos 67 dias após emergência, foram medidas a altura das plantas, matéria seca da parte aérea e composição elementar das folhas. Em comparação ao calcário, o lodo alcalinizado promoveu maior produção de matéria seca da planta nos solos argilosos. O lodo de esgoto alcalinizado aplicado aos solos resultou em maiores teores de Zn e P na parte aérea da planta do que o calcário, enquanto ambos os corretivos reduziram os teores de K e Mn na parte aérea. A relação Fe/Mn mostrou ser muito efetivo para explicar sintomas foliares que foram observados sob condição de elevada acidez. O lodo alcalinizado apresentou desempenho superior quanto à nutrição e promoção do crescimento do feijoeiro no solo argiloso.

Methanogens Diversity during Anaerobic Sewage Sludge Stabilization and the Effect of Temperature

Anaerobic sludge stabilization is a commonly used technology. Most fermenters are operated at a mesophilic temperature regime. Modern trends in waste management aim to minimize waste generation. One of the strategies can be achieved by anaerobically stabilizing the sludge by raising the temperature. Higher temperatures will allow faster decomposition of organic matter, shortening the retention time, and increasing biogas production. This work is focused on the description of changes in the community of methanogenic microorganisms at different temperatures during the sludge stabilization. At higher temperatures, biogas contained a higher percentage of methane, however, there was an undesirable accumulation of ammonia in the fermenter. Representatives of the hydrogenotrophic genus Methanoliea were described at all temperatures tested. At temperatures up to 50 °C, a significant proportion of methanogens were also formed by acetoclastic representatives of Methanosaeta sp. and acetoclastic representatives of the order Methanosarcinales. The composition of methanogens in the fermenter significantly changed at 60 °C when typically thermophilic species, like Methanothermobacter marburgensis, appeared. A decrease in the diversity of methanogens was observed, and typical hydrogenotrophic methanogenic archaea isolated from fermenters of biogas plants and anaerobic wastewater treatment plants represented by genus Methanoculleus were no longer present.