Pure Sewage Sludge Research Articles

An Example of a New Approach, New Assessment, New Statistical Inference, and New Conclusions from the Published Research by Nikipelova, O., Pyliak, N., & Hodorchuk, V. (2023). Organic fertilizers in increase of hazelnut yield. Interdepartmental Thematic Scientific Collection of Phytosanitary Safety, (69), 118-128. https://doi.org/10.36495/1606-9773.2023.69.118-128.

Background: The declining availability of traditional organic fertilizers and the need for sustainable waste management solutions have sparked interest in alternative nutrient sources for agriculture. This study investigates the potential of sewage sludge-based biofertilizers in hazelnut (Corylus avellana L.) cultivation, addressing both agricultural productivity and environmental concerns. Objective: To evaluate and compare the effects of sewage sludge-based biofertilizers with traditional organic fertilizers on soil agrochemical properties and assess their environmental safety in hazelnut plantations in the Southern Steppe of Ukraine. Methods: A two-year field experiment (2021-2022) was conducted, comparing six treatments: control (no fertilizer), cattle manure, chicken manure, two formulations of sewage sludge-based biofertilizers, and pure sewage sludge. Soil samples were analyzed for easily hydrolyzable nitrogen, mobile phosphorus and potassium, organic matter content, and ecotoxicity. Advanced statistical analyses, including ANOVA, Tukey's post-hoc tests, paired t-tests, and correlation analyses, were employed to assess treatment effects and temporal changes. Results: Statistically significant differences were observed between fertilizer treatments for all major nutrients (p < 0.05). Sewage sludge-based Biofertilizer No. 1 demonstrated superior performance in increasing soil phosphorus content compared to traditional organic fertilizers (306.30 mg/kg vs. 174.75 mg/kg for cattle manure, p < 0.05). All organic fertilizers, including biofertilizers, significantly improved soil nitrogen content over the two-year period (p < 0.05). Potassium levels showed a significant increase (13.41% year-over-year, p < 0.05), while changes in nitrogen and phosphorus levels suggested positive trends but did not reach statistical significance. Importantly, ecotoxicity levels remained low (E < 1.5) across all treatments, indicating minimal short-term environmental risk. Conclusions: This study provides compelling evidence for the potential of sewage sludge-based biofertilizers as effective and environmentally safe alternatives to traditional organic fertilizers in hazelnut cultivation. The findings have significant implications for sustainable agriculture, waste management, and circular economy practices. However, long-term studies are recommended to fully assess the cumulative effects on soil health, crop productivity, and potential contaminant accumulation. This research contributes to the development of innovative, sustainable fertilization strategies that can address both agricultural productivity and environmental conservation needs.

Treatment of Produced Water Using Prepared Activated Carbon-Based Sewage Sludge

Removal of organic pollutants and metal ions from produced water by adsorption, using prepared activated carbon (AC) from sewage sludge, with chemical activations using NaOH, KOH and ZnCl2 separately and pyrolysis at different temperatures (500, 600 and 700 °C). Pure sludge and prepared ACs were analyzed using FTIR and XRD. The results showed 18% crystallinity compared to that of commercial AC, which has 44% crystallinity. The results of FTIR demonstrate that the properties of the post-treated affect the final products depending on the method used and that it contains similar functional groups to those present in the commercial AC, but at a higher peak intensity. Adsorption treatments were carried out at 25, 35 and 45 °C solution temperatures. The results showed that the removal of pollutants from produced water using prepared AC with all types of chemical activations reached 99.5%, such as commercial AC with 0.06 g dosage of adsorbent at pyrolysis temperatures of 500 and 600 °C and a solution temperature of 25 °C. The obtained results refer to the mechanism of exothermic reaction and physical adsorption. It was observed that despite the lower dosage of adsorbent of 0.01 g, a sufficient treatment of pollutants was achieved. This reveals the effectiveness of using sewage sludge as a cheap adsorbent. Also, using pure sewage sludge, the adsorption data showed a 95.2% removal of the pollutants. This result indicated that pure sludge has an efficient adsorption capacity and can be utilized as a cheap and environmentally friendly material. For the removal of manganese and cadmium metal ions from the produced water, the resultant data showed that more than 90% of manganese was adsorbed and more than 97% of cadmium was adsorbed, especially when using pure sewage sludge and prepared activated carbon with NaOH chemical activation at pyrolysis temperatures of 500 °C and 600 °C.

Bubbling fluidized bed co-combustion and co-gasification of sewage sludge with agricultural residues with a focus on the fate of phosphorus

In this work, the fate of the ash-forming elements during bubbling fluidized bed combustion and gasification of P-rich sewage sludge (SS) and mixtures with either Si-K-rich wheat straw (WS) or K-Ca-rich sunflower husks (SH) were investigated. The focus of the study was assessing the feasibility of using fuel blends in fluidized bed systems and potential P recovery from the resulting ashes. The used fuels were pure SS and mixtures including 90 wt.% WS (WSS) and 85 wt.% SH (SHS). The analyzed operating conditions were combustion (930–960 °C, λ: 1.2–1.5) and gasification (780–810 °C, λ: 0.4–0.7) in a 5 kW bench-scale reactor. Residual ash and char fractions were collected from different parts of the 5 kW bubbling fluidized bed (bed, cyclone, filter) and analyzed by CHN, SEM/EDS, XRD, and ICP-AES.The conversion of the fuel mixtures achieved a steady state under the used process conditions except for the combustion of WSS, which led to the formation of large bed agglomerates with the bed material. The morphology of ash samples after combustion showed that SS fuel pellets mostly maintained their integrity during the experiment. In contrast, the ash and char particles from fuel mixtures were fragmented, and larger quantities were found in the cyclone, the filter, or on interior reactor surfaces. The fate of P was dominated by crystalline Ca-dominated whitlockites in all ash fractions, partially including K for the fuel mixtures SHS and WSS. 76–81 % of ingoing P was found in the bed residue after combustion and gasification of the SS-fuel. After conversion of the fuel mixtures SHS and WSS, the share was lower at 22–48 %, with larger shares of P in the entrained fractions (25–34 %). The quantity of identified crystalline compounds was lower after gasification than combustion, likely due to the limited interaction of ash-forming elements in the residual CHN matrix. Altogether, the results show that fuel mixtures of sewage sludge with agricultural residues could expand the fuel feedstock and enable P recovery. This may be used in the fuel and process design of upscaled fluidized bed processes or systems employing both combustion and gasification.

Application of circular economy in wastewater treatment using biochar based adsorbent derived from sewage sludge

The Circular Economy intends to reuse wastewater and recover resources and energy from the sludge in the wastewater sector. The conversion of sewage sludge into biochar by pyrolysis technique is a sustainable, environmentally friendly option for sewage sludge management. In the current work, biochar was produced by co-pyrolyzing sewage sludge and coconut shell, and it was then utilized as an adsorbent to eliminate methylene blue (the model pollutant) from wastewater. The sewage sludge is abundant in functional groups and metal ions, and the addition of coconut shells increased the porosity of the adsorbent. The biochar produced by mixing coconut shell and sewage sludge in the ratio1:1 showed higher adsorption capacity compared to biochar obtained from pure sewage sludge; hence the co-pyrolyzed biochar was used for further studies. The morphology and functional groups present on biochar were examined using SEM and FTIR analysis. The kinetics and mechanism of methylene blue adsorption was adequately explained by the pseudo-second-order kinetic model. Using the Langmuir isotherm model, the maximal adsorption capacity of the methylene blue dye on biochar was observed to be 31.64 mg/g.

Phytoextraction of arsenic, nickel, selenium and zinc from sewage sludge: from laboratory to pilot scale

AimsThe present study aimed at: (i) verifying the suitability of pure sewage sludge (SS) as growing medium for the hyperaccumulator species (Pteris vittata, Odontarrhena chalcidica, Astragalus bisulcatus and Noccaea caerulescens); (ii) evaluating the removal of As, Ni, Se and Zn operated by the chosen species; (iii) estimating the potential metal yields (bio-ore production) and connected monetary rewards in a small-scale field experiment.MethodsHyperaccumulator plants were first tested under controlled conditions, on three different SS (P1, P2, P3) characterized by the presence of one or more contaminants among As, Ni, Se and Zn. P1 sludge was then chosen for a small-scale field experiment. Hyperaccumulator seedlings were transferred on SS and cultivated for 16 weeks before harvesting.ResultsAll hyperaccumulator species grew healthy on P1 SS, with A. bisulcatus and O. chalcidica reaching an average biomass of 40.2 and 21.5 g DW/plant. Trace metal concentrations in aerial parts were: As (P. vittata) 380 mg/kg DW, Ni (O. chalcidica) 683 mg/kg DW, Se (A. bisulcatus) 165 mg/kg DW, Zn (N. caerulescens) 461 mg/kg DW. The total removal of As, Ni, Se and Zn from SS due to phytoextraction was 5.8, 19, 18, 29% respectively.ConclusionsThis study demonstrated that phytoextraction can be applied to SS for the removal contaminants while recovering valuable metals. Se and As were identified as the most promising target element, while Ni and Zn removal was poorly efficient under the present experimental conditions.

Trace Metal Accumulation and Phytoremediation Potential of Four Crop Plants Cultivated on Pure Sewage Sludge

Phytoremediation is a viable strategy to remove trace metal contaminants from sewage sludge but still is poorly investigated. The aim of this study was to quantify the trace metal removal of B. napus, B. juncea, H. annuus, Z. mays grown on pure sewage sludge. Each species was grown on six different sewage sludge for 8 weeks and sludge were analysed for trace metal content and physico-chemical characteristics. Our results confirmed that all the tested sludge supported plant growth. The tested sludge showed a plant vigorousness lower (46% of sludge) or similar/increased (54% of sludge) compared to control treatment. B. juncea and B. napus were the most efficient species in the bioaccumulation, of trace metals. The average percentage of metals removed by the selected species was 0.2% for As, 0.85% for Cd, 0.09% for Cr, 0.36% for Cu, 0.36% for Ni, 4.2% for Se, 1.2% for Zn. In conclusion, our results showed that phytoremediation can be applied to sewage sludge, despite the chosen species have low efficiency in trace element removal. Further studies using hyperaccumulator species are needed which may lead to a higher efficiency of the process opening up new possibilities for the management strategies of this waste.

Influence of soil structure of newly formed agricultural landscape of recultivated landfill of municipal solid waste on its humidity

The objective of the study is to justify the influence of different proportions of sewage sludge introduction into the soil of a newly formed agricultural landscape on a recultivated landfill site taken out of operation. To achieve this goal it is necessary to monitor the dynamics of humidity in the recultivated areas during the growing season of 2020 under actual weather conditions. The areas were recultivated applying various technologies and the irrigation mode was introduced on the Area No. 2. This area is characterized by three types of soil: test - ordinary chernozem; a mixture of chernozem and sewage sludge; pure sewage sludge. Area No. 1 is pure wastewater sludge. The studies on humidity dynamics show that the humidity is changeable in different periods of the growing season, but in the areas with wastewater sediments, the field humidity is higher than in the test area. Thus, it can be concluded that the introduction of sewage sludge influences the structure of the resulting soil, which favorably impacts its water-retaining capacity.

Single Pellet Combustion of Sewage Sludge and Agricultural Residues with a Focus on Phosphorus

Recycling of phosphorus in combination with increased utilization of bioenergy can mitigate material and global warming challenges. In addition, co-combustion of different fuels can alleviate ash-related problems in thermal conversion of biomass. The aim of this study is to investigate the ash transformation reactions of mainly P in co-combustion of P-rich sewage sludge (SS) with K-rich sunflower husks (SH) and K- and Si-rich wheat straw (WS). Single pellets of 4 mixtures (10 and 30 wt % SS in WS and 15 and 40 wt % SS in SH) and pure SS were combusted in an electrically heated furnace at process temperatures relevant for fluidized bed combustion (800 and 950 °C). Collected ash fractions were analyzed by inductively coupled plasma techniques, ion chromatography, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and X-ray diffraction. Thermodynamic equilibrium calculations were performed to interpret the results. Over 90% of K and P was found to be captured within the residual ash with 30–70% P in crystalline K-bearing phosphates for mixtures with low amounts of SS (WSS10 and SHS15). The significant share of K and P in the amorphous material could be important for P recovery. For the lower percentage mixtures of SS (WSS10 and SHS15), P in crystalline phases was mainly found in K-whitlockite and CaKPO4. For the higher percentage SS mixtures, most of P was found in whitlockites associated with Fe and Mg, and no crystalline phosphates containing K were detected. For P recovery, co-combustion of the lower SS mixtures is favorable, and they are suggested to be further studied concerning the suitability for plant growth.

Evaluating the Effect of Sewage Sludge on Bioactive Components of Momordicacharantia

Momordicacharantia L. belongs to the family Cucurbitaceae. This plant has widely been reported for use in traditional medical systems for the treatment of diabetes, rheumatism, intestinal gas and malaria. The ethnicity of M. charantiais Asia, Africa and some parts of Europe where it is considered edible. Sewage sludge, a by-product of waste water treatment plant, contains several nutrients. These nutrients are known as beneficial for the better growth and good yield of the plants. The objective of this study is to optimize soil with different ratios of sewage sludge for increased growth of bioactive components in M. charantia. The plant was grown at six places; in soil containing 20%, 40%, 60% and 80% sewage sludge ratio as well as in pure soil and in pure sewage sludge. Fruit harvesting was carried out after 75 days. Methanol extract of M. charantia (Fruit) was subjected to analysis using GC-MS. Comparative quantification of 7,11-hexadecadienal, oleic Acid and stigmasterol were carried out. It has been found that the soil containing 60% sewage sludge yielded maximum quantity of 7,11-hexadecadienal, oleic Acid and stigmasterol. Therefore, optimization of soil with different ratios of sewage sludge is carried out and 60% ratio of sewage sludge in soil is recommended for the promising growth of Momordicacharantia.

Evaluating the Effect of Sewage Sludge on Bioactive Components of Momordicacharantia

Momordicacharantia L. belongs to the family Cucurbitaceae. This plant has widely been reported for use in traditional medical systems for the treatment of diabetes, rheumatism, intestinal gas and malaria. The ethnicity of M. charantiais Asia, Africa and some parts of Europe where it is considered edible. Sewage sludge, a by-product of waste water treatment plant, contains several nutrients. These nutrients are known as beneficial for the better growth and good yield of the plants. The objective of this study is to optimize soil with different ratios of sewage sludge for increased growth of bioactive components in M. charantia. The plant was grown at six places; in soil containing 20%, 40%, 60% and 80% sewage sludge ratio as well as in pure soil and in pure sewage sludge. Fruit harvesting was carried out after 75 days. Methanol extract of M. charantia (Fruit) was subjected to analysis using GC-MS. Comparative quantification of 7,11-hexadecadienal, oleic Acid and stigmasterol were carried out. It has been found that the soil containing 60% sewage sludge yielded maximum quantity of 7,11-hexadecadienal, oleic Acid and stigmasterol. Therefore, optimization of soil with different ratios of sewage sludge is carried out and 60% ratio of sewage sludge in soil is recommended for the promising growth of Momordicacharantia.

Desorption characteristics of phosphate and ammonium from sludge-based biochar

ABSTRACT It is effective to adsorb phosphate and ammonium from water by sludge-based biochar, while the desorption performance has not been studied systematically. Biochar in this study was prepared through the co-pyrolysis of sludge and walnut shells to remove and from water. The desorption characteristics of and from the post-adsorption sludge-based biochar were investigated. The effects of the adsorption condition (concentration of adsorption solution) and desorption conditions (pH value of desorption solution and desorption temperature and time) on desorption performance were examined. Several techniques were performed to characterise the properties of the post-adsorption sludge-based biochar. The adsorption amount of the pure sewage sludge biochar (SBC) for and the biochar derived from the co-pyrolysis of sewage sludge and walnut shell with the mixing ratio of 3:1 (MBC3-1) for were 14.19/ 23.75 mg/g and 9.28/ 16.23 mg/g, respectively, when the concentrations of the adsorbates were 100 and 500 mg/L. The desorption experiments showed that the acidic condition (pH = 2) was beneficial for and desorption. The highest desorption ratio reached 7.58% for and 2.18% for . The desorption of was endothermic, whereas that of was exothermic. The desorption amounts of and decreased and increased, respectively, with the increase in desorption time. This study of the desorption characteristics of and in sludge-based biochar provides a theoretical basis for the subsequent utilisation of sludge-based biochar.

Innovative substrates for sugarcane seedling production: Sewage sludges and rice husk ash in a waste-to-product strategy

Recent advances in the sucroenergy production chain include a new way of planting sugarcane based on a method of seedling propagation which requires a significant amount of substrate. Since the sucroenergy sector has been noted as having cleaner energy production, it is imperative that sustainable substrates suitable for the production of sugarcane seedlings be developed. Therefore, the main objective of this study was to develop innovative substrates with solar-dried sewage sludges and rice husk ash to compose substrates for sugarcane seedling production. Batches of sewage sludges were collected in open drying beds from three different municipal wastewater treatment plants from the Rio Grande do Sul State, Brazil: from Passo Fundo city (treated by anaerobic digestion), from Rio Grande city (aerobic digestion) and from Santa Maria city (aerobic digestion). Rice husk ash was obtained from a rice processing industry in the Pelotas industrial region in southern Brazil. The content of trace elements and the pathogenicity of pure sewage sludge (SS) were analyzed. The nutrient content of SS and rice husk ash (RHA) was determined. Twelve substrates with differing ratios of SS, RHA, and vermiculite were formulated to evaluate the subsequent development of sugarcane seedlings. Chemical and physical attributes were determined in all substrates and compared to a commercial substrate. The experiment was conducted in a greenhouse using mini-setts of sugarcane of the RB867515 genotype. Fifteen days after planting the seedlings were evaluated for stalk diameter, shoot height, shoot dry weight and root, and the Dickson quality index was determined. Sewage sludge showed low levels of heavy metals and pathogenic organisms and high contents of nutrients, especially nitrogen, phosphorus and micronutrients such as Zn and Cu, showing promising suitability as a substrate component for seedling production. In general, substrates of all tested proportions of SS and RHA promoted greater shoot and root dry weight and a superior Dickson Quality Index than the commercial substrate used as reference, except for the formulation containing 87.5 % SS. The viability of combining sludges from municipal wastewater treatment plants and rice husk ash into one product was confirmed using a set of biometric attributes and nutrient tissue contents obtained from the production of sugarcane seedlings.

Thermochemical equilibrium study of ash transformation during combustion and gasification of sewage sludge mixtures with agricultural residues with focus on the phosphorus speciation

The necessity of recycling anthropogenically used phosphorus to prevent aquatic eutrophication and decrease the economic dependency on mined phosphate ores encouraged recent research to identify potential alternative resource pools. One of these resource pools is the ash derived from the thermochemical conversion of sewage sludge. This ash is rich in phosphorus, although most of it is chemically associated in a way where it is not plant available. The aim of this work was to identify the P recovery potential of ashes from sewage sludge co-conversion processes with two types of agricultural residues, namely wheat straw (rich in K and Si) and sunflower husks (rich in K), employing thermodynamic equilibrium calculations. The results indicate that both the melting behavior and the formation of plant available phosphates can be enhanced by using these fuel blends in comparison with pure sewage sludge. This enhanced bioavailability of phosphates was mostly due to the predicted formation of K-bearing phosphates in the mixtures instead of Ca/Fe/Al phosphates in the pure sewage sludge ash. According to the calculations, gasification conditions could increase the degree of slag formation and enhance the volatilization of K in comparison with combustion conditions. Furthermore, the possibility of precipitating phosphates from ash melts could be shown. It is emphasized that the results of this theoretical study represent an idealized system since in practice, non-equilibrium influences such as kinetic limitations and formation of amorphous structures may be significant. However, applicability of thermodynamic calculations in the prediction of molten and solid phases may still guide experimental research to investigate the actual phosphate formation in the future.

BIOCARVÃO DO BIOSSÓLIDO DA ESTAÇÃO DE TRATAMENTO DE ESGOTO DE PRESIDENTE PRUDENTE-SP

Biosolidis a material rich in organic matter and other nutrients of agronomic importance such as nitrogen and phosphorus. Its end is almost always in landfills. Therefore, its transformation into biochar by the pyrolysis process would be a way to associate its inherent benefits to biochar, enabling a more appropriate final destination. Given this work the objective was to produce biochar in order to evaluate the viability of use in agriculture. The biochar was produced on a laboratory scale at different temperatures and therefore the characterization of the final product was performed. As a result, the material has proven to be rich in organic matter as temperature increases, thinning the material and increasing the specific surface making the alkaline pH serving as carbon sequestration. Thus, with the constant concern of sewage sludge 47Colloquium Exactarum, v. 11, n4, Out-Dez. 2019, p.46 –61. DOI: 10.5747/ce.2019.v11.n4.e296production, biochar proved to be more efficient than pure sewage sludge for agricultural application.

Biochar produced from the co-pyrolysis of sewage sludge and walnut shell for ammonium and phosphate adsorption from water

Pyrolysis of sewage sludge to obtain biochar is an environmentally friendly method of sewage sludge utilization. In this study, sewage sludge and walnut shell were co-pyrolyzed to produce biochar, which was utilized in the adsorption of ammonium and phosphate from water. Brunauer–Emmett–Teller analysis, X-ray diffraction spectroscopy, scanning electron microscopy, and Fourier transform infrared techniques were applied to analyze the physical and chemical properties of the biochar. The sewage sludge-based biochar consisted of rich metal oxides and functional groups, and the addition of walnut shell was beneficial for the development of porous structure. When the mixing ratio of sewage sludge and walnut shell was 3:1, the derived biochar (MBC3-1) showed a high adsorption capacity for NH4+ in neutral or weak alkaline water. Pure sewage sludge biochar (SBC) was the best option for the adsorption of PO43− in a wide pH range of water. The adsorption of NH4+ and v on MBC3-1 and SBC were controlled by intraparticle diffusion and pseudo-second-order kinetic models, respectively. Isothermal studies indicated that multiple adsorption processes occurred in the adsorption of NH4+ and PO43−, and the maximum adsorption capacity of NH4+ and PO43− reached 22.85 mg/g and 303.49 mg/g on MBC3-1 and SBC, respectively. Thermodynamic analysis confirmed the exothermic and endothermic nature for NH4+ and PO43− adsorption on biochar, respectively.

CO2 adsorption on biochar from co-torrefaction of sewage sludge and leucaena wood using microwave heating

Microwave co-torrefaction of sewage sludge and leucaena wood was carried out to produce biochar for the adsorption of CO2. Three mixing ratios of sewage sludge and leucaena wood were 75:25, 50:50, and 25:75. The individual and blended biomass sample were torrefied at a microwave power level of 250 W. Mass and energy yields decreased whereas carbon and fixed carbon contents increased with increasing mixing ratio of leucaena wood. The biochar with higher carbon content could be capable of adsorbing more CO2 molecules. The adsorption capacity of pure leucaena wood biochar was approximately 53 mg/g, almost four times as that of pure sewage sludge biochar. The more fraction of leucaena wood in the blend would possess an adverse effect on the composition or property of biochar, resulting in lower CO2 adsorption capacity. Four kinetic models were applied to analyze the reaction kinetics of CO2 adsorption on biochar. The CO2 adsorption on biochar was best fitted by the pseudo-second-order kinetic model. The relatively low correspondence with the intraparticle diffusion kinetic model may imply that the CO2 adsorption on biochar is more governed by adsorption reaction.

Sewage sludge compost as a substrate for croton seedlings production

The floricultural industry is always searching for new and low-cost materials to use as substrate for crop growth and development. Sewage sludge is an organic solid waste from sewage treatment and it has a good potential to be used as an organic fertilizer and/or substrate conditioner. The research aimed to evaluate the rooting and growth of Codiaeum variegatum ‘Andreanum’ (red variety) and Codiaeum variegatum ‘Punctatum’ (yellow variety) cuttings cultivated in the potting media: PM1 - 100% commercial potting media used as control (CS), PM2 - 100% organic compost of sewage sludge + sugarcane bagasse (SSSB), PM3 - 50% CS + 50% SSSB, PM4 - 100% organic compost of sewage sludge + eucalyptus bark (SSEB) and PM5 - 50% CS + 50% SSEB. After 90 days of experimentation the chemical analysis of the substrate solution (pH, electric conductivity, P, K, Ca, Mg, S, Na, B, Cu, Mn and Zn) and number of shoots, shoot fresh and dry mass, plant cutting fresh and dry masses, root fresh and dry masses, total fresh and dry masses and, length of the largest root were analyzed. Our results showed that sewage sludge compost can be used as a substrate for rooting and growth of croton cuttings when mixed with commercial substrate. The use of the pure sewage sludge compound with sugarcane bagasse or eucalyptus bark prejudiced croton cuttings to root.

Enhanced Biogas Production in Pilot Digesters Treating a Mixture of Sewage Sludge, Glycerol, and Food Waste

Anaerobic co-digestion of a ternary mixture of sewage sludge with food waste and residual glycerol was evaluated in pilot scale units, with the aim to increase methane production in sludge anaerobic digesters at sewage treatment plants. Two pilot scale anaerobic digesters (useful volume of 320 L) operated simultaneously for 60 days at room temperature (24 °C on average). One digester received only sludge in the feed, and the other received the ternary mixture. The feeding routine of the digesters respected a semi-continuous mode. The units continuously promoted the mixing of the sludge through a bottom-up recirculation system with a hydraulic retention time of 30 d. The digester fed with just sewage sludge had greater instability during the whole period of operation, producing about 3 L d–1 of biogas with 23% methane, volatile solids (VS) removal of 65.3%, and methane yield (MY) of 98.5 LN CH4 kg–1VS add. On the other hand, the digester fed with the ternary mixture produced 21 L d–1 of biogas with 43% methane, VS removal of 73.4%, and MY of 174.5 LN CH4 kg–1VS add. The mass and energy balances showed that through methane recovery, the ternary mixture substrate contributed to the production of 12 times more energy than that of digesters fed with pure sewage sludge.

Ecotoxicological and microbiological assessment of sewage sludge associated with sugarcane bagasse

Sewage sludge (SS) obtained after sewage treatment process may contain several toxic substances. Bioremediation can decrease the toxicity of the sludge, mainly when it is associated with stimulant agents, such as sugarcane bagasse (B). Samples of pure SS (SSP); SS+B; SS+Soil; and SS+B+Soil were bioremediated for 1, 3, and 6 months (T1, T2, and T3, respectively). After each period, the cytotoxic, genotoxic, and mutagenic potentials of the solid samples and their respective aqueous extracts (aqueous eluate and percolate water) were evaluated by the Allium cepa test. A microbiological analysis of the samples was also performed after each period tested. All solid samples of SS+B (in T1, T2, and T3) and the solid sample of SSP (treatment T3) showed a significant decrease of cell division (cytotoxic effects). The aqueous eluate extracts of SS+B (T1 and T3) and SSP (T2 and T3) induced cytotoxic effect. The solid sample of SS+B (T2 and T3) and aqueous extracts of SSP (T1) were genotoxic, indicating a harmful effect of SS on A. cepa, even after 6 months of bioremediation. There was an alternation in the microbial community both in diversity and in abundance, with the predominance of nonfermenting gram-negative bacilli. The tested bioremediation periods were not sufficient for the complete detoxification of SS, and the use of B did not seem to contribute to the degradation of the pollutants to inert compounds. These data emphasize that a specific relationship should exist between the sludge characteristic and the biostimulating agent used to promote a more efficient bioremediation. These results suggest the necessity to study longer periods of biodegradation and the use of other decomposing agents for greater safety and sustainability for the agricultural use of this residue.

Reprodução e desenvolvimento de minhocas gigante africana (Eudrilus eugeniae) em Lodo de Esgoto produzido na cidade de Gurupi, Estado do Tocantins

Este trabalho teve como objetivo avaliar a reprodução e o desenvolvimento de minhocas (Eudrilus eugeniae) em diferentes diluições de lodo de esgoto produzido na cidade de Gurupi, Estado do Tocantins, sob condições de sombreamento natural em mata de cerrado e umidade controlada. O experimento foi realizado entre os meses de Abril a Julho de 2011. As avaliações ocorreramapós 30, 60 e 90 dias, quando se comparou as quantidades de nascimentos e mortes de minhocas em três tipos de substratos: T1 = lodo de esgoto puro; T2 = 75% lodo de esgoto + 25% de casca de arroz e T3 = 50% lodo de esgoto +50% de casca de arroz, mantidas com 80% de umidade através de irrigação artificial. A maior quantidade de nascimentos ocorreu no tratamento T2 aos 30 dias e não foram observadas diferenças nas quantidades finais de minhocas nos três tratamentos e nas três épocas avaliadas. O tratamento T3proporcionou os maiores valores médios reprodutivos. Observou-se uma tendência em aumentar a biomassa das minhocas conforme se diluiu as concentrações de lodo de esgoto.