Large Amounts Of Sewage Sludge Research Articles

Substrates based on composted sewage sludge for land recultivation

Increasing a large amounts of sewage sludge in Ukraine is an urgent environmental problem that requires the selection of an effective strategy for their disposal. The usage of sludge composting technology leads to the restoration of sludge as a resource and is cost-effective and environmentally sustainable compared to the method of landfilling. The purpose of this research is to carry out bioindication tests of growth substrates based on composted sewage sludge with the subsequent possibility of their usage in the technology of recultivation of landfills for municipal solid waste. The experiment was performed on four types of compost with different modifications of the natural sorbent - zeolite. During the experiment the average percentage of germination of polygamous ryegrass plants (Lolium perenne L.) was determined in the investigated substrates. The mass and length of the aboveground part of the plant and roots were also measured. The results showed that the addition of natural sorbent to substrates has a positive effect on growth and development of plants. This investigation was conducted in accordance with the current norms of national standards of Ukraine: DSTU 7369 (2013), "Wastewater. Requirements for wastewater and its sediments for irrigation and fertilization"; DSTU ISO 11269-1 (2004), "Soil quality. Determination of the effect of pollutants on soil flora. Part 1: Method for determining the inhibitory effect on a root growth"; DSTU ISO 11269-2 (2002), "Soil quality. Determination of the effect of pollutants on soil flora. Part 2: Effects of Chemicals on Germination and Growth of Higher Plants". The experiment was conducted on four types of compost with different modifications of the natural sorbent - zeolite in percentage amounts: 0; 2.5; 5; 7.5, dark-grey gilded soil was used as a control element. In the experiment, the average percentage of germination of polygamous ryegrass plants (Lolium perenne L.) on the studied substrates was determined. The mass and length of the aboveground part of the plant and roots were also measured. The first sprouts of ryegrass began to appear on the 7th day of the experiment. The highest average value on the seventh day of germination was 90% in the control sample with 5% of sorbent content and in K2 substrate in the sample with 7.5% sorbent content. However, the germination of plants in substrates K3 and K4 occurred later compared with substrates K1, K2, and control. For substrate K1 in the sample with a sorbent content of 5%, plant germination was the highest and was 100%. The highest average value of ryegrass stem length is observed in variant K4 in the sample with 0% zeolite content and in variant K1 in the sample without zeolite content the lowest average value of stem length was observed. The K3 and K4 variants have a more developed root system compared to other variants. Based on the obtained data it can be assumed that the most optimal universal component for creating a growth substrate is variant K3 (mixture of "newly picked" and "old" SS) which has not so developed aboveground part but has very branched root system that allows to adapt to various environmental factors and in combination with a small proportion of natural sorbents can be effective for the recultivation of MSW landfills, which in its turn minimizes the need to use a fertile soil layer.

The Influence of Municipal Wastewater Treatment Technologies on the Biological Stabilization of Sewage Sludge: A Systematic Review

Various wastewater treatment technologies are available today and biological processes are predominantly used in these technologies. Increasing wastewater treatment systems produces large amounts of sewage sludge with variable quantities and qualities, which must be properly managed. Anaerobic and aerobic digestion and composting are major strategies to treat this sludge. The main indicators of biological stabilization are volatile fatty acids (VFAs), volatile solids (VS), the carbon/nitrogen (C/N) ratio, humic substances (HS), the total organic carbon (TOC), the carbon dioxide (CO2) evolution rate, the specific oxygen uptake rate (SOUR), and the Dewar test; however, different criteria exist for the same indicators. Although there is no consensus for defining the stability of sewage sludge (biosolids) in the research and regulations reviewed, controlling the biological degradation, vector attraction, and odor determines the biological stabilization of sewage sludge. Because pollutants and pathogens are not completely removed in biological stabilization processes, further treatments to improve the quality of biosolids and to ensure their safe use should be explored.

Risk Assessment and Potential Analysis of the Agricultural Use of Sewage Sludge in Central Shanxi Province.

The agricultural use of sewage sludge has become an economic disposal method used worldwide. However, heavy metals contained in sewage sludge have become the crucial limiting factors for this way of disposal. This study showed that regulatory limit values are not enough to determine whether sewage sludge is suitable for agricultural use; risk assessment and potential analysis should be applied. Correlation analysis and hierarchical cluster analysis (HCA) should also be performed to identify heavy metals’ sources and show their influence on sewage sludge utilization. Samples were collected from 13 wastewater treatment plants (WWTPs) located in central Shanxi Province. Results indicated that the mean contents of heavy metals in sewage sludge were all less than the limit threshold of China. According to the monomial potential ecological risk coefficient (), the agricultural use of sewage sludge had low ecological risks for all heavy metals, except for Hg and Cd. Based on the potential ecological risk index (RI), only three stations had moderate risk, other nine stations all had higher potential risk. The mean potentials by all heavy metals were all beyond 10 years, which is the limit of the maximum application time specified by China. Combining all heavy metals, only one station’s potential was less than 10 years. Although the contents of heavy metals were all within the threshold values, large quantities of sewage sludge are not suitable for agricultural use. Coal-related industries, which were the main sources of Hg and Cd, greatly affected the agricultural use of sewage sludge.

The Development of the Membrane-Filter Press System(MFPS) by Utilizing Ultrasonic Waves for Treating Sewage Sludge

Sewage treatment plants produce large amounts of sewage sludge yearly in Korea. In this study, a Membrane-Filter Press System (MFPS) using ultrasonic waves was developed to treat sewage sludge at the Seonam sewage treatment plant in Seoul. The MFPS consists of an ultrasonic extractor, a polymer injection tank, a membrane-filter press, and a centrate tank for improving sludge dewatering and phosphorus recovery. Two types of sewage sludge were used: digested raw sludge and digested excess sludge. In lab-scale experiments with an ultrasonic extractor, the concentration of phosphorus was 214.9 mg/L at 50 rpm after sonication at 500 W for 20 min, which was around 4.9 times higher than non-treated sludge. In the pilot-scale experiment, dewaterability of the digested raw and excess sewage sludge was investigated in the MFPS under three sets of operating conditions involving modifier injection, ultrasonication, and polymer injection. it was found that the moisture content of the dewatered digested raw and excess sewage sludge cakes was reduced to 50.5% and 54.3%, respectively. Lowering the moisture content reduced the total volume of the sludge by approximately 40% compared to a conventional centrifugal dehydrator. It is expected that the MFPS will reduce the disposal cost of sludge and offers a sustainable solution for recycling resources.

Co-Pyrolysis of Sewage Sludge and Wetland Biomass Waste for Biochar Production: Behaviors of Phosphorus and Heavy Metals.

Large amounts of sewage sludge (SS) and wetland plant wastes are generated in the wastewater treatment system worldwide. The conversion of these solid wastes into biochar through co-pyrolysis could be a promising resource utilization scheme. In this study, biochar was prepared by co-pyrolysis of SS and reed (Phragmites australis, RD) using a modified muffle furnace device under different temperatures (300, 500, and 700 °C) and with different mixing ratios (25, 50, and 75 wt.% RD). The physicochemical properties of biochar and the transformation behaviors of phosphorus (P) and heavy metals during the co-pyrolysis process were studied. Compared with single SS pyrolysis, the biochar derived from SS-RD co-pyrolysis had lower yield and ash content, higher pH, C content, and aromatic structure. The addition of RD could reduce the total P content of biochar and promote the transformation from non-apatite inorganic phosphorus (NAIP) to apatite phosphorus (AP). In addition, co-pyrolysis also reduced the content and toxicity of heavy metals in biochar. Therefore, co-pyrolysis could be a promising strategy to achieve the simultaneous treatment of SS and RD, as well as the production of value-added biochar.

Microbial mechanism underlying high methane production of coupled alkali-microwave–H2O2–oxidation pretreated sewage sludge by in-situ bioelectrochemical regulation

The stabilization and disposal of the large amounts of sewage sludge pose a worldwide challenging problem. To solve this problem, the technical feasibility of coupled alkali-microwave–H2O2–oxidation pretreatment with in-situ bioelectrochemical regulation was used for enhancing sludge biodegradability and methane productivity. The optimum condition of the combined pretreatment was pH 10.0 ± 0.1, microwave 700 W and H2O2 0.4 g/g TS. In this case, soluble chemical oxygen demand (SCOD) of pretreated sludge was increased from initial 330.9 ± 10.0 to 3328.8 ± 49.6 mg/L. The highest accumulative methane yield of 234.3 mL CH4/g VS was obtained for pretreated sludge at the cathodic potential of −0.8 V vs. Ag/AgCl, increasing by 4.3-, and 1.9-fold compared with the raw and pretreated sludge, respectively. The microbial community analysis further provided a compelling evidence that bioelectrochemical regulation stimulated the growth of the functional microorganisms, especially in protein-degrading (Firmicutes), polysaccharides-utilizing (Chloroflexi), electroactive (Geobacter, and Desulfomicrobium) and methane-producing (Methanobacterium) microorganisms. In addition, pH adjustment of pretreated sludge by addition of H2SO4 could further enrich the abundance of microbial community and build a strong syntrophic interaction, accordingly provoking the hydrolysis and subsequent methane production. The result of this study will contribute to the establishment of an efficient sludge stabilization and bioenergy recovery strategy.

Geotechnical properties of clayey soil improved by sewage sludge ash

ABSTRACT Rapid urbanization has resulted in the production of large quantities of sewage sludge over worldwide. The disposal of sewage sludge in landfills or open areas is not considered as an environmentally friendly solution. Therefore, the use of sewage sludge as ash can provide a better solution in geotechnical applications. Keeping this in view, this study investigates the possibility of using sewage sludge ash (SSA) to improve the geotechnical properties of soft clay soil. The sewage sludge ash (SSA) is attained by burning the sludge for 2 h at 900°C. The tests conducted on the clayey soil are specific gravity, standard Proctor test, sieve analysis, Atterberg limits, CBR test and unconfined compression test. Three curing times were used for the untreated soils and soils treated with sewage sludge ash (SSA) which are 3 days, 14 days and 28 days. The sewage sludge ash (SSA) was mixed with the soil at different percentages by weight of the soil at 10%, 15% and 20% of dry soil weight. The results showed that the sludge ash increases the unconfined compressive strength of the soft soil at 3, 14, 28-day curing time. The bearing capacity of the soil decreases after adding SSA at the first, but curing time led to improve the bearing capacity of clayey soil after adding SSA and the percentage of SSA of 10% gave the optimum value of CBR. The results indicated that a better performance of the unconfined shear strength was obtained at 28-day curing time. The findings of this research indicate that sewage sludge ash (SSA) can be used to improve the soft clayey soil and further reduce the environmental risks associated with this substantial. Implications: Rapid urbanization has resulted in the production of large quantities of sewage sludge over worldwide. The disposal of sewage sludge in landfills or open areas is not considered as an environmentally friendly solution. Therefore, the use of sewage sludge as ash can provide a better solution in geotechnical applications. Keeping this in view, this study investigates the possibility of using sewage sludge ash (SSA) to improve geotechnical properties of soft clay soil. In this paper, Sewage Sludge Ash (SSA) is recycled as a new type of chemical addition to soft clay soil and used as a stabilizer to improve a clayey soil. This study proposes that a percent of the total amount of clay to be reinforced is replaced with sewage sludge ash (sewage sludge ash plus soil) in order to achieve the need of improvement in the geotechnical properties of clayey soil and make use of industrial wastes. The sewage sludge ash (SSA) is attained by burning the sludge for 2 h at 900°C. The tests conducted on the clayey soil are specific gravity, standard Proctor test, sieve analysis, Atterberg limits, CBR test, and unconfined compression test. Three curing times were used for the untreated soils and soils treated with sewage sludge ash (SSA) which are 3 days, 14 days, and 28 days. The sludge ash (SSA) was mixed with the soil at different percentages by weight of the soil at 10%, 15%, and 20% of dry soil weight. The results showed that the sludge ash increases the unconfined compression strength of the soft soil at 3, 14, 28-day curing time. The bearing capacity of the soil decreases after adding SSA at the first, but curing time led to improve the bearing capacity of clayey soil after adding SSA and the percentage of SSA of 10% gave the optimum value of CBR. The results indicated that a better performance of the unconfined shear strength was obtained at 28-day curing time. The findings of this research indicate that sewage sludge ash (SSA) can be used to improve the soft clayey soil and further reduce the environmental risks associated with this substantial.

Heavy Metals and Macronutrients Concentrations in Sewage Sludge Obtained from Decentralized Treatment Facility, Machakos Town, Kenya

With the increase of global population, wastewater treatment facilities face a major challenge of managing the large quantities of sewage sludge produced in urban areas. Due to this challenge many wastewater treatment plants have opted for use of sewage sludge as organic fertilizer to boost agricultural production. In Machakos Decentralized Treatment Facility (DFT), sewage sludge is usually sold to locals as fertilizer to boost crop production within the municipality. However, sewage sludge produced in municipal wastewater treatment plants is known to contain various heavy metals that may limit its usage as agricultural fertilizer. Studies have shown that sewage sludge has been associated with heavy metals which are linked to harmful effects on humans and environmental health. This study investigated the levels of various heavy metals and macronutrients from sewage sludge obtained from Machakos town wastewater treatment plant to test its suitability for use as fertilizer. Sewage sludge samples were obtained from the treatment plant at Mitheu and transported to Nairobi Agricultural Research Laboratory (NARL) for analysis of heavy metals (Cu, Zn, Mn, and Fe) and macronutrients (N, P, Ca, Mg and K). The results for the heavy metals were Zn=171.13±237mg/kg; Fe=17,877±15,700mg/kg; Mn=445.67±213mg/kg and Cu=41.1±16.71mg/kg) while the macronutrients were K=0.17±0.09%, P=1.26±1.75%, N=0.74±0.47%, Ca=0.48±0.72% and Mg=0.10±0.06%. The heavy metal concentrations were below Kenya Bureau of Standards (KEBS) and international permissible limits for sewage sludge application in agriculture and therefore deemed safe. The study concluded that the sewage sludge from Machakos Decentralized Treatment Facility is rich in nutrients and thus a potential fertilizing agent that can be used to boost plant growth in agricultural farms. However, it was noted that not all the wastewater produced in Machakos town gets into the DFT for treatment. Therefore, the study recommended that the county government of Machakos should endeavor to enlarge the small DFT treatment plant to accommodate the large quantities of wastewater generated within the town.

Evaluation the Efficiency of Stabilization Technique of Organic Soil by Comparison Between the Two Stabilizers

Sewage treatment plants produce large quantities of sewage sludge as by-products, as the sludge contains elements harmful to environment. Such study investigated of utilizing different percentages of sewage (7, 14 and 21%) of soil weight. The stabilization / solidification process was used to improve the properties of the organic soil and meet its requirements. This technique was the use of traditional and nontraditional additives such as cement and styrene acrylic. The major objective of that research is to evaluate efficiency of stabilized soils through comparison of stabilizers. The organic soil was prepared and stabilizers were added in different proportions (3, 6 and 9%) for the purpose of the tests. Mechanical tests (Unconfined Compressive Strength (UCS) and Hardness) were used for the soil sample to estimate the best mixing and obtaining higher strength. Through outcome of the UCS and hardness tests, cement was most effective agent of styrene in terms of improving the properties, strength and hardness of the organic treated soil.

Study of Evolution of Microbiological Properties in Sewage Sludge-Amended Soils: A Pilot Experience.

Large amounts of sewage sludge are generated in urban wastewater treatment plants and used as fertilizer in agriculture due to its characteristics. They can contain contaminants such as heavy metals and pathogenic microorganisms. The objective of this research work is to study, in real conditions, the evolution of microbial concentration in agricultural soils fertilized by biologically treated sewage sludge. The sludge (6.25 tons Ha−1) was applied in two agricultural soils with different textures and crops. A microbiological (total coliforms, Escherichia coli, Staphylococcus aureus, Enterococcus sp., Pseudomonas sp., Salmonella sp. and total mesophylls) and physical-chemical characterization of the sludge, soils and irrigation water were carried out. The evolution of these parameters during sowing, growth and harvesting of crops was studied. Initially, sewage sludge had a higher concentration of microorganisms than soils. Irrigation water also contained microorganisms, fewer than sewage sludge amendment but not negligible. After amendment, there were no differences in the microbiological evolution in the two types of soil. In general, bacterial concentrations after crop harvest were lower than bacterial concentrations detected before sewage sludge amendment. Consequently, the application of sludge from water treatment processes did not worsen the microbiological quality of agricultural soil in this study at real conditions.

Effects of Sewage Sludge Amendments on the Growth and Physiology of Sweet Basil

Currently, wastewater treatment plants produce large amounts of sewage sludge. Due to the rich content of organic matter and minerals, sewage sludge can be used as soil amendments for eroded soils. The aim of this work was to assess sewage sludge (SS) in combination with an eroded soil (ES) collected from the North Eastern Romania as growth substrate for sweet basil, and their effect on basil growth and physiology. The experiment was conducted in a greenhouse under controlled environment conditions. The tested substrates were: (1) eroded soil, ES; (2) mixture of eroded soil (15%) + sewage sludge, ES + SS (85%); and (3) sewage sludge, SS (100%). Three types of parameters were studied: morphological traits, physiological, and biochemical parameters. The maximum quantum yield of Photosystem II Fv/Fm was reduced in basil leaves grown on eroded soil (0.80) and was close to the normal value in ES + SS (0.83). Chlorophyll a and the carotenoids content were higher for plants grown on SS and significantly higher for those grown in ES + SS compared with the one of plants grown on ES. The fresh biomass yield and height of basil increased with 44% and 34.5% under ES + SS over ES. Total phenolic content was higher in plants grown on ES (7.34 mg/g dry weight Gallic acid equivalent), which also led to an increased antioxidant activity (44.4%) evaluated by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method. Fourier-Transform Infrared (FT-IR) (4000–400 cm−1) spectra of basil did not show significant qualitative differences among the plants from different treatments. The results of this study demonstrated that SS application led to the improvement of the basil morpho-physiological parameters, allowing the growth of basil on ES + SS.

A study of solubilization of sewage sludge by hydrothermal treatment

The use of activated sludge process for biological treatment of domestic and industrial wastewaters generates large amounts of sewage sludge, which is regarded as problematic biowaste. Conventional waste treatment methods such as landfilling and ocean pumping have been used to dispose the unwanted sludge, but this practice is no longer recommended due to serious secondary pollution and strict environmental regulations. Hydrothermal treatment represents a promising alternative that has attracted attention in recent years. In this study, batch experiments of hydrothermal treatment of domestic sewage sludge were conducted under varying conditions (temperature of 150–300 °C, reaction time of 0.5–3.0 h, and sludge concentration of 5–30 g/L). A statistical study of the responses, including disintegration degree and concentration of dissolved compounds, was performed using a response surface methodology. Optimal conditions for hydrothermal treatment of sewage sludge were obtained through mathematical modeling.

Biodegradation of nonylphenol during aerobic composting of sewage sludge under two intermittent aeration treatments in a full-scale plant

The urbanization and industrialization of cities around the coastal region of the Bohai Sea have produced large amounts of sewage sludge from sewage treatment plants. Research on the biodegradation of nonylphenol (NP) and the influencing factors of such biodegradation during sewage sludge composting is important to control pollution caused by land application of sewage sludge. The present study investigated the effect of aeration on NP biodegradation and the microbe community during aerobic composting under two intermittent aeration treatments in a full-scale plant of sewage sludge, sawdust, and returned compost at a ratio of 6:3:1. The results showed that 65% of NP was biodegraded and that Bacillus was the dominant bacterial species in the mesophilic phase. The amount of NP biodegraded in the mesophilic phase was 68.3%, which accounted for 64.6% of the total amount of biodegraded NP. The amount of NP biodegraded under high-volume aeration was 19.6% higher than that under low-volume aeration. Bacillus was dominant for 60.9% of the composting period under high-volume aeration, compared to 22.7% dominance under low-volume aeration. In the thermophilic phase, high-volume aeration promoted the biodegradation of NP and Bacillus remained the dominant bacterial species. In the cooling and stable phases, the contents of NP underwent insignificant change while different dominant bacteria were observed in the two treatments. NP was mostly biodegraded by Bacillus, and the rate of biodegradation was significantly correlated with the abundance of Bacillus (r = 0.63, p < 0.05). Under aeration, Bacillus remained the dominant bacteria, especially in the thermal phase; this phenomenon possibly increased the biodegradation efficiency of NP. High-volume aeration accelerated the activity and prolonged the survival of Bacillus. The risk of organic pollution could be decreased prior to sewage sludge reuse in soil by adjusting the ventilation strategies of aerobic compost measurements.

Incorporation of paper sludge in clay brick formulation: Ten years of industrial experience

The large amounts of sewage sludge (11million tonnes in Europe in 2005) produced in paper manufacturing plants require the introduction of recycling and/or alternative recovery solutions to minimize the amounts of generated waste, such as its use in soil remediation or in the cement industry. A feasible alternative to valorize that waste is the use of paper sludge as raw material in the production of structural ceramic or clay bricks.Previous studies tried to incorporate sewage sludge from different sources into ceramic matrices, unfortunately with little success in the final result for most types of sludge. However, those experiments carried out using as additive sludge from the paper industry succeeded in producing a material suitable for the red ceramic industry.In this paper, binary mixtures of clay and paper sludge under different formulations were produced and their physico-chemical properties were studied. Increasing the paper sludge content in the clay mixture provides the material with improved properties regarding its thermal and acoustic insulation, but in turn it decreases its mechanical strength. However, this fragility of the material is compensated by an increased ductility. Regarding metal leaching, the studied ceramics have no environmental restrictions as far as their use as building material is concerned, as the obtained results were virtually identical to those for the blank samples (100% clay). Results showed that the presence of dichloromethane (373.2μgm−3) and propanone (61.2μgm−3) in the samples with added sludge was relatively relevant with respect to concentrations in samples made of 100% clay. All monocyclic aromatics detected showed a concentration level far below their odor threshold. In general, thus, it can be concluded that volatile organic compound (VOC) emissions during firing of the new ceramic material do not involve any particular problem. Finally, the experience obtained after more than 10years of industrial production of this new mixed ceramic product was also analyzed. This analysis allowed confirmation that clay brick production with incorporation of paper sludge waste is a feasible solution from a technical point of view. As a key outcome, this fact has helped the reduction in a large proportion the amount of sludge produced by the Spanish paper industry ending up in landfills.

The process research of anaerobic flora disintegrating excess sludge

Large amounts of sewage sludge are produced from activated sludge processes, causing serious secondary pollution. Thus, the development of stable, safe, and low-cost methods to dispose excess sludge has gradually become a popular research topic. The anaerobic/anaerobic microorganism method shows good prospects for industrialization because of its advantages such as low cost and no secondary pollution. The current study focuses on the effect of anaerobic microorganisms on waste activated sludge during anaerobic fermentation. In this research, the changes of organic compounds, extracellular enzymes, and size distributions in the process of anaerobic flora disintegrating excess sludge were measured to clarify the disintegrating process. In various disintegrating products, COD was observed to be suitable for characterizing the degree of sludge disintegration. The disintegration efficiency of anaerobic flora was 34.86% or 3.5 times higher than that of the anaerobic environment. Lipase played an important role in breaking cell walls. There was a dynamic equilibrium in the sludge disintegration and reuse of disintegration products. The change in size distribution showed that easily degraded materials accumulated and large granular sludge was destroyed. The present study lays the foundation for future studies on the optimization of conditions for sludge disintegration.

Influence of Wastewater Treatment and The Method of Sludge Disposal on the Gasification Process

Abstract Municipal wastewater treatment results in the production of large quantities of sewage sludge, which requires proper environmentally accepted management before final disposal. Sewage sludge is a by-product of current wastewater treatment technologies. Sewage sludge disposal depends on the sludge treatment methods used in the wastewater treatment plant (anaerobic or aerobic digestion, drying, etc.). Taking into consideration presented given this information, a study concerning the effects of wastewater treatment processes and sewage sludge drying method on the sewage sludge gasification gas parameters was performed. Gasification is a prospective alternative method of sludge thermal treatment. For the purpose of experimental investigations, a laboratory fixed bed gasifier installation was designed and built. Two types of sewage sludge feedstock, SS1 and SS2, were analyzed. Sewage sludge SS1 came from a wastewater treatment plant operating in the mechanical and biological system while sewage sludge SS2 was collected in a mechanical, biological and chemical wastewater treatment plant with simultaneous phosphorus precipitation. The sludge produced at the plants was subject to fermentation and then, after being dehydrated, dried in a cylindrical drier on shelves heated up to 260ºC (sewage sludge SS1) and using hot air at a temperature of 150ºC in a belt drier (sewage SS2). The analysis shows that the sewage sludge properties strongly depend on the wastewater sources and the wastewater treatment processes. The gasification results, presented as a function of the amount of gasification agent, show that the greater oxygen content of SS1 caused a reduction in the reaction temperature. Paradoxically, this effect caused an increase in the quantity of combustible components in the gas. As expected, increasing the air flow rate caused a decrease in the heating value of the gas produced. A higher amount of oxidizer increases the amounts of noncombustible species and the volumetric fraction of nitrogen, thus reducing the heating value of the obtained gas. The higher hydrogen content in SS1 affects the gasification gas composition. As a result, combustible components are the majority of the syngas.

Thermal behaviour of sewage sludge in pyrolysis process

Municipal wastewater treatment results in the production of large quantities of sewage sludge. The proper treatment and disposal of sewage sludge is one of the important environmental issues. The pyrolysis of three samples of sewage sludge was studied by a thermogravimetric analyser and a fixed bed reactor at the temperature of 30–800°C. Sewage sludge was collected from Shaoxing wastewater treatment plant in China. The heating value of sewage sludge was at the range of 10·8–12·9 kJ g−1. The rate of pyrolysis as a function of temperature was obtained for different heating rates. The results showed that the pyrolysis of sludge can be divided into four stages: evaporation, decomposition of small molecular weight matter, main decomposition and final decomposition range. Gas chromatographic analysis showed that the gas released during the pyrolysis process mainly included H2O, CO, CO2 and CH4. The effect of metal oxides (CaO, Fe2O3) on the pyrolysis of sewage sludge was also investigated.

Biosolid stockpiles are a significant point source for greenhouse gas emissions

The wastewater treatment process generates large amounts of sewage sludge that are dried and then often stored in biosolid stockpiles in treatment plants. Because the biosolids are rich in decomposable organic matter they could be a significant source for greenhouse gas (GHG) emissions, yet there are no direct measurements of GHG from stockpiles. We therefore measured the direct emissions of methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) on a monthly basis from three different age classes of biosolid stockpiles at the Western Treatment Plant (WTP), Melbourne, Australia, from December 2009 to November 2011 using manual static chambers. All biosolid stockpiles were a significant point source for CH4 and N2O emissions. The youngest biosolids (<1 year old) had the greatest CH4 and N2O emissions of 60.2 kg of CO2-e per Mg of biosolid per year. Stockpiles that were between 1 and 3 years old emitted less overall GHG (∼29 kg CO2-e Mg−1 yr−1) and the oldest stockpiles emitted the least GHG (∼10 kg CO2-e Mg−1 yr−1). Methane emissions were negligible in all stockpiles but the relative contribution of N2O and CO2 changed with stockpile age. The youngest stockpile emitted two thirds of the GHG emission as N2O, while the 1–3 year old stockpile emitted an equal amount of N2O and CO2 and in the oldest stockpile CO2 emissions dominated. We did not detect any seasonal variability of GHG emissions and did not observe a correlation between GHG flux and environmental variables such as biosolid temperature, moisture content or nitrate and ammonium concentration. We also modeled CH4 emissions based on a first order decay model and the model based estimated annual CH4 emissions were higher as compared to the direct field based estimated annual CH4 emissions. Our results indicate that labile organic material in stockpiles is decomposed over time and that nitrogen decomposition processes lead to significant N2O emissions. Carbon decomposition favors CO2 over CH4 production probably because of aerobic stockpile conditions or CH4 oxidation in the outer stockpile layers. Although the GHG emission rate decreased with biosolid age, managers of biosolid stockpiles should assess alternate storage or uses for biosolids to avoid nutrient losses and GHG emissions.

Heavy metals availability and soil fertility after land application of sewage sludge on dystroferric Red Latosol

Sewage sludge is the solid residue obtained from urban sewage treatment plants. It is possible to use the sludge in a sustainable way as fertilizer and as soil conditioner due to its high levels of organic matter and nutrients. Besides pathogens and volatile organic compounds, the residue may also contain heavy metals which may accumulate and contaminate crops and the food chain. The aim of this study was evaluates the changes in the fertility of dystrophic Red Latosol and in the availability of heavy metals following application of sewage sludge. It was assessed whether organic matter supplied to the soil as large amounts of sewage sludge would decrease availability of heavy metals in the soil due to of insoluble compounds formation. From this, an experiment was carried out in polyethylene pots using lettuce plant for test. Sewage sludge were applied to the soil in concentrations equivalent to 60, 120 and 180 t ha-1, and a control without sludge, in four replicates, in a completely randomized design. The results show that sewage sludge led to an increase of organic matter contents, of the cation exchange capacity (CEC) and of nutrients found in the soil. It also improved plant growth up to a concentration of 120 t ha-1. Availability of heavy metals, however, was reduced in sludge concentrations starting with 120 t ha-1.

Obtaining biostimulant products for land application from the sewage sludge of small populations

Large amounts of sewage sludge are generated in wastewater treatment plants during the water purification process. In small populations – defined as urban settlements with less than 2000 population equivalent – sewage sludge is normally produced in anaerobic systems (e.g. septic tanks, Imhoff tanks or anaerobic ponds) or in extended aeration systems. According to the European Directives 86/278/EEC and 2006/12/EC, sewage sludge must be treated before its final fate. Although there are various alternatives, land application of sewage sludge after its composting has been widely promoted because of its high nutrient content. However, the employment of composted sludge as a soil amendment has some limitations, including social rejection. In this paper, a hydrolytic process for obtaining an agricultural biofertiliser from sewage sludge has been assessed. The enzymatic hydrolysis of sludge produced two by-products: an insoluble paste and a nutrient-enriched liquid that constituted the fertilising product. This biofertiliser had higher contents of organic matter, proteins, potassium (K) and sulphur (S) compared to the fresh sludge. Protein content was characterised by a low molecular size, thus increasing the bioavailability of nitrogen (N). Further, high levels of enzymatic activity were detected in soil after the addition of the obtained biofertiliser.