Search Results (9)

The study presents the research results on the rejected water generated in dewatering sludge stabilised in Autothermal Thermophilic Aerobic Digestion (ATAD) technology. The research was carried out in three municipal wastewater treatment plants (WWTPs), with a capacity of 1500 to 3260 m³ d⁻¹ and a sludge node capacity of 835 to 2000 kg DM d⁻¹. The mean content of Kjeldahl nitrogen (TKN) in the rejected water samples taken from each object ranged from 485 to 1573 mg N L⁻¹, ammonium nitrogen 318 to 736 mg N L⁻¹, and the average concentration of total phosphorus ranged from 96 to 281 mg P L⁻¹. The average content of organic matter expressed as five-day biological oxygen demand (BOD₅) ranged from 205 to 730 mg O₂ L⁻¹, while chemical oxygen demand (COD) ranged from 767 to 4884 mg O₂ L⁻¹. The study determined the kinetics of the biochemical decomposition of organic matter, assuming that it follows the first-order equation. The average reaction rate constant k in subsequent treatment plants was estimated at 0.424, 0.513 and 0.782 d⁻¹. The R² coefficient determining the model’s adjustment to empirical values was not lower than 0.952. The organic matter biodegradability index average values ranged from 0.17 to 0.26. Full article

This manuscript analyzed the process of autothermal thermophilic aerobic digestion (ATAD) used in installations of municipal sewage treatment plants in Poland. Additionally, solutions for sludge management and the parameters of operating installations were presented. Attention was also put to the energy consumption of the process, where the energy consumption for 1 m³ of sludge treated was between 18.4 and 27.79 kWh. The amount of sewage flowing into the analyzed plants was between 1500 and 14,000 m³/d. On the basis of research carried out in the years 2003–2019 in the selected plants, the characteristics of sludge after the ATAD process were presented. The parameters that determine the usefulness of the sludge as an organic fertilizer were indicated above all. The content of total nitrogen, which was from 2.4 to 8.1% of dry matter, ammonium nitrogen, which was from 0.8 to 1.8% of dry matter, and total phosphorus, which was from 1.1 to 4.2% of dry matter, recommended using sludge for fertilization. It was also pointed out that sewage sludge should be regularly tested for the dynamics of changes in chemical composition and biological parameters. These are the factors that increase risk and limit the use of sludge for fertilization. Full article

Sewage sludge is a by-product of the municipal wastewater treatment process. The amount of sewage sludge generated in treatment plants in Poland and other European countries is constantly growing. Due to the growing environmental awareness, legal requirements are being established that require the appropriate treatment of sludge before it can be used for natural purposes. Therefore, operators are looking for the best solutions to ensure proper sewage sludge preparation. More and more ATAD (auto-thermophilic sewage sludge stabilization) installations are being built in Poland, which allow for simultaneous stabilization and hygienization of sludge. However, this process contributes to the formation of leachate, which is discharged into the biological reactors of municipal sewage treatment plants. The leachate after the ATAD process has a complex organic substance and is characterized by large loads of total nitrogen and total phosphorus. Biological wastewater treatment processes can be ineffective for such specific pollutants returned in ATAD leachate. Thus far, no research has been undertaken to analyze the problem presented. Full article

This paper presents the process of autothermal thermophilic aerobic digestion (ATAD). The installations used in municipal sewage treatment plants in Poland were reviewed. The adopted solutions for sludge management and parameters of operating installations were presented. Attention was also drawn to the energy consumption of the process. On the basis of research carried out in the years 2003–2019 in the plants in question, the characteristics of sludge after the ATAD process were presented. The parameters that determine the usefulness of the sludge as an organic fertilizer are indicated above all. Full article

Autothermal thermophilic aerobic digestion (ATAD) is a microbial fermentation process characterized as a tertiary treatment of waste material carried out in jacketed reactors. The process can be carried out on a variety of waste sludge ranging from human, animal, food, or pharmaceutical waste where the addition of air initiates aerobic digestion of the secondary treated sludge material. Digestion of the sludge substrates generates heat, which is retained within the reactor resulting in elevation of the reactor temperature to 70–75 °C. During the process, deamination of proteinaceous materials also occurs resulting in liberation of ammonia and elevation of pH to typically pH 8.4. These conditions result in a unique microbial consortium, which undergoes considerable dynamic change during the heat-up and holding phases. The change in pH and substrate as digestion occurs also contributes to this dynamic change. Because the large reactors are not optimized for aeration, and because low oxygen solubility at elevated temperatures occurs, there are considerable numbers of anaerobes recovered which also contributes to the overall digestion. As the reactors are operated in a semi-continuous mode, the reactors are rarely washed, resulting in considerable biofilm formation. Equally, because of the fibrous nature of the sludge, fiber adhering organisms are frequently found which play a major role in the overall digestion process. Here, we review molecular tools needed to examine the ATAD sludge consortia, what has been determined through phylogenetic analysis of the consortia and the nature of the dynamics occurring within this unique fermentation environment. Full article

Autothermal thermophilic aerobic digestion (ATAD) is an advanced sewage sludge treatment which allows compliance with increasingly demanding regulations. Concerning sludge pasteurization, a certain average temperature must be assured in the digester during batch treatment. Aeration flow is the variable most manipulated to regulate the digester temperature. Additionally, the manipulation of the batch sludge flow—which is related to the solid-retention-time—is considered to improve temperature regulation despite variations in air and sludge temperatures and the variability of raw sludge organic content. Thus, a dual-input control structure was provided where the aeration and solid-retention-time contributed as faster and slower inputs, respectively. Two controllers intervened, and the set-point for the batch average temperature was chosen to meet the minimum effluent quality established by the US regulations or European recommendations, considering that lower set point temperatures save aeration costs. A set-point for the aeration allowed us to achieve an extra goal, which aimed at either reducing operation costs or increasing production rates. The two feedback controllers were designed following the robust control methodology known as quantitative feedback theory (QFT). Improvements were compared with single-input (aeration-flow) control strategy and open-loop control strategy. Simulations were performed on a benchmark non-linear simulation model for ATAD. Full article

The degradation of sludge solids in an insulated reactor during Autothermal Thermophilic Aerobic Digestion (ATAD) processing results in auto-heating, thermal treatment and total solids reduction, however, the ability to eliminate pathogenic organisms has not been analysed under large scale process conditions. We evaluated the ATAD process over a period of one year in a two stage, full scale Irish ATAD plant established in Killarney and treating mixed primary and secondary sludge, by examining the sludge microbiologically at various stages during and following ATAD processing to determine its ability to eliminate indicator organisms. Salmonella spp. (pathogen) and fecal-coliform (indicator) densities were well below the limits used to validate class A biosolids in the final product. Enteric pathogens present at inlet were deactivated during the ATAD process and were not detected in the final product using both traditional microbial culture and molecular phylogenetic techniques. A high DNase activity was detected in the bulk sludge during the thermophilic digestion stage which may be responsible for the rapid turn over of DNA from lysed cells and the removal of mobile DNA. These results offer assurance for the safe use of ATAD sludge as a soil supplement following processing. Full article

Molecular analysis of the bacterial community structure associated with sludge processed by autothermal thermophilic aerobic digestion (ATAD), was performed using a number of extraction and amplification procedures which differed in yield, integrity, ability to amplify extracted templates and specificity in recovering species present. Interference to PCR and qPCR amplification was observed due to chelation, nuclease activity and the presence of thermolabile components derived from the ATAD sludge. Addition of selected adjuvant restored the ability to amplify community DNA, derived from the thermophilic sludge, via a number of primer sets of ecological importance and various DNA polymerases. Resolution of community profiles by molecular techniques was also influenced by the ATAD sludge extraction procedure as demonstrated by PCR-DGGE profiling and comparison of taxonomic affiliations of the most predominant members within 16S rRNA gene libraries constructed from ATAD DNA extracted by different methods. Several modifications have been shown to be necessary to optimize the molecular analysis of the ATAD thermal niche which may have general applicability to diversity recovery from similar environments. Full article

Abstract: The pattern of biodegradation and the chemical changes occurring in the macromolecular fraction of domestic sludge during autothermal thermophilic aerobic digestion (ATAD) was monitored and characterised via solid-state ¹³C-NMR CP-MAS. Major indexes such as aromaticity, hydrophobicity and alkyl/O-alkyl ratios calculated for the ATAD processed biosolids were compared by means of these values to corresponding indexes reported for sludges of different origin such as manures, soil organic matter and certain types of compost. Given that this is the first time that these techniques have been applied to ATAD sludge, the data indicates that long-chain aliphatics are easily utilized by the microbial populations as substrates for metabolic activities at all stages of aerobic digestion and serve as a key substrate for the temperature increase, which in turn results in sludge sterilization. The ATAD biosolids following treatment had a prevalence of O-alkyl domains, a low aromaticity index (10.4%) and an alkyl/O-alkyl ratio of 0.48 while the hydrophobicity index of the sludge decreased from 1.12 to 0.62 during the treatment. These results have important implications for the evolution of new ATAD modalities particularly in relation to dewatering and the future use of ATAD processed biosolids as a fertilizer, particularly with respect to hydrological impacts on the soil behaviour. Full article