Sludge Disposal Costs Research Articles

Comprehensive Management of Water Resources: A Step-By-Step Path Towards a Sustainable Campus At The U.D.C.A (Bogotá, Colombia)

Universities are recognized as essential agent of change since future decision-makers related to sustainability are going and will pass through their classrooms. This circumstance becomes an excellent opportunity to demonstrate, with example, and instill in the students how these types of organizations control and approach implementing practices that guarantee sustainability and the appropriate use of resources over time. The Universidad de Ciencias Aplicadas y Ambientales has undertaken different actions related to the Integrated Water Resources Management (IWRM) on campus since 1990. This work focuses on the actions carried out by the Integrated Environmental Management System (latest institutional management model) between the 2014-2016 period to improve the university campus's IWRM (drinking water and wastewater management) from a systemic point of view. The actions implemented were part of the project: Reusing treated water at the University's Wastewater Treatment Plant (WWTP). This project included the following objectives: 1) Reduce the volume and economic costs of sludge water disposal; 2) Reduce drinking water consumption; and 3) Promote environmental education about water resources in students of the different programs of the University. The results were: 1) A decrease of 68.3% in volume and 69.5% in costs of sludge water disposal; 2) A 41.2% saving in drinking water consumption; and 3) 2,475 members of the university community impacted by issues related to the management of water resources.

Study of Characteristics and Heavy Metals Migration During Co-Combustion of Coal and Sludge

Study of Characteristics and Heavy Metals Migration During Co-Combustion of Coal and Sludge

Performance assessment and economic aspects for water reclamation from UASB reactor effluent: Influence of coagulant type and membrane pore size

ABSTRACT This paper investigates the influence of coagulant type in coagulation, flocculation and sedimentation processes and membrane pore size on the performance and economic aspects of water reclamation from UASB reactor effluent. The methodology involved laboratory-scale experiments using two different coagulant types (a modified tannin coagulant, TANm, and a polyaluminum chloride, PACl) and membrane filtration tests with microfiltration (MF) and ultrafiltration (UF). Compared to PACl, TANm had a smaller effect on the pH, consumed less alkalinity, and generated less sludge. However, PACl was more efficient in removing turbidity (89–97%), organic matter (70–72%), and phosphorus within the dosage range of 25 to 100 mg.L−1. Both membranes achieved high removal rates for turbidity and organic matter. Despite the higher flux decay, the MF system could have higher operating flux and lower fouling resistance. The operating costs were higher for the C/F systems, which was attributed to the cost of coagulants and sludge disposal. The system with MF membranes had a lower total cost, and the estimated payback period for the investment was between 0.73 to 0.24 years, based on the values charged for reuse water. This information can be used to optimize the design and operation of UASB-based water reclamation systems.

Synchronous in-situ sludge reduction and enhanced denitrification through improving electron transfer during endogenous metabolisms with Fe(Ⅱ) addition

The creation of large amounts of excess sludge and residual nitrogen are critical issues in wastewater biotreatment. This study introduced Fe(II) into an oligotrophic anaerobic reactor (OARFe) that was implemented to modify an anoxic-oxic process to motivate in-situ sludge reduction and enhance denitrification under an effective electron shuttle among organic matter, nitrogen, and Fe. The addition of 15 mg L−1 Fe(II) resulted in a sludge reduction efficiency reached 32.0% with a decreased effluent nitrate concentration of 33.3%. This was mostly attributed to the electron transfer from Fe(II) to organic matters and nitrogen species in OARFe. The participation of Fe(II) led to the upregulation of Geothrix and Terrimonas, which caused active organic matter hydrolysis and cell lysis to stimulate the release of extracellular polymeric substances (EPS) and substance transfer between each layer of EPS. The higher utilization of released bioavailable dissolved organic matter improved endogenous denitrification, which can be combined with iron autotrophic denitrification to realize multiple electron donor-based nitrogen removal pathways, resulting in an increased nitrate removal rate of 58.2% in the absence of external carbon sources. These functional bacteria associated with the transformation of nitrogen and carbon and cycling between ferrous and ferric ions were enriched in OARFe, which contributed to efficient electron transport occurred both inside and outside the cell and increased 2,3,5-triphenyltetrazolium chloride electronic transport system activity by 46.9%. This contributed to the potential operational costs of chemical addition and sludge disposal of Fe-AO being 1.9 times lower than those of conventional A2O processes. These results imply that the addition of ferrous ions to an oligotrophic anaerobic zone for wastewater treatment has the potential for low-cost pollution control.

Behavior of Sludge Dewaterability and Nutrient Contents after Treatment with Cellulose-Based Flocculants with Combined PTS and Catalytic Behavior of Sludge towards Tetracycline Degradation

Wastewater treatment plants are increasingly interested in adopting inorganic coagulants and organic flocculants in their sludge treatment process since sludge disposal costs more than half of the overall operational costs. This study synthesized poly titanium sulfate (PTS) by different molar ratios and used the best one with cellulose-based flocculants for sludge conditioning. PTS synthesized with a 1:2 molar ratio showed the lowest capillary suction time (CST) of sludge and was selected for further studies with cellulose-based flocculants. As bio-based flocculants have gained popularity due to current environmental problems, cationized cellulose-based flocculants (Ce-CTA) were used in this work with or without PTS for sludge treatment. After coagulation–flocculation, dewaterability of sludge enhanced, and the Lowry and Anthrone method was used to assess proteins and polysaccharides. Next, metal content and nutrients such as total phosphorus, phosphate, and nitrate were measured by ICP-OES and IC, and we found promising results of phosphate especially at pH 3. Higher total phosphorus content was found at pH 3 and 9, and even at pH 6 after PTS or PTS+Ce-CTA treatment. In addition, PTS-treated sludge materials also showed catalytic behavior, suggesting a new research avenue for future development. Based on this study, the PTS+Ce-CTA combination is promising for sludge treatment and nutrient recovery, along with the possibility for the further valorization of the sludge materials.

An integrated approach to vivianite recovery from waste activated sludge

The waste activated sludge (WAS) of wastewater treatment system is often rich in phosphorus (P), which is a basic element of human life and could use up in the near future. This study proposed an integrated approach to efficiently recover P as vivianite from WAS and simultaneously enhance the sludge dewaterability. The raw WAS was first acidified using FeCl3, which was then fed to anaerobic fermenter for Fe3+ reduction. After fermentation, a technology named acid-elutriation was introduced to convert Fe and P from solid phase to liquid phase and concomitantly enhance the liquor-solid separation. Finally, vivianite was obtained via sludge eluate neutralization. The enhanced sludge dewaterability not only increases the recovery efficiency of Fe and P but also decreases the cost of sludge disposal.

Process Economy of Alternative Fuel Production from Sewage Sludge and Waste Celluloses Biomass

The treatment and disposal of sewage sludge is one of the most important and critical problems of wastewater treatment plants. 8.7 million tonnes of dry matter of sewage sludge were produced annually in the European Union in the year 2020. Due to the fact that sewage sludge contains a large number of substances that are not beneficial for human health, the conditions for sludge management will be significantly tightened in the EU countries. One option for sludge liquidation is the production of biofuel in a form of granules or pellets from sewage sludge enriched by waste celluloses. The achieved results show that the resulting quality of such alternative biofuel is fully comparable to conventional fossil fuels. The economic analysis is based on the simulation of cash flows associated with the implementation of the project over the lifetime and the calculation of levelised cost (LCOE). Results shows (under the current economic situation) that solar dryer technology ensures the lowest LCOE at the level of 26 EUR/GJ in fuel. If the LCOE of the alternative biofuel includes the price of the saved emission allowance and the future costs of sewage sludge disposal, the resulting price is directly competitive with lignite. The results thus clearly show that there is an ecological and economically competitive substitute for solid fossil fuels, which may be an important step for the future use of local combustion sources such as district heating plants.

Effect of pH, Salinity, Dye, and Biomass Concentration on Decolourization of Azo Dye Methyl Orange in Denitrifying Conditions

A recent study by the current authors found simultaneous decolourization and mineralization of high concentrations of methyl orange (500 mg/L) in an anoxic up-flow reactor in denitrifying conditions. To supplement this work, various batch reactor studies were carried out to study the effect of (i) pH (4 to 9), (ii) salinity (1 g/L NaCl to 10 g/L NaCl), (iii) dye concentration (100 mg/L to 1000 mg/L), (iv) biomass concentration (0.3 g/L to 0.21 g/L); on the process, and (iv) kinetics of decolourization in denitrifying conditions. The adapted mixed microbial consortium, originally sourced from the activated sludge process, was capable to simultaneously remove colour, COD, and NO3−-N under denitrifying conditions, even at high methyl orange (MO) concentrations of 1000 mg/L at 84 h. Although the decolourization was possible for wide ranges of pH, better performance was obtained at alkaline pH levels. The decolourization performance increased when biomass concentration increased and was not affected by salinity up to 10 g/L NaCl. This may have been due to enhanced lyses of biomass at high salt concentrations. Batch kinetic studies showed that the MO decolourization followed first-order kinetics, with a rate constant of 0.0612 h−1. Results of this study may help in the future application of textile effluent treatments, using a high biomass retention reactor in denitrifying conditions with minimum sludge disposal costs.

Enhanced Sludge Dewaterability by Efficient Oxidation of α-Mn2O3/Peroxymonosulfate: Analysis of the Mechanism and Evaluation of Engineering Application

Sludge dewatering reduces huge volumes of sludge, which can help save costs of subsequent sludge treatment and disposal. Extracellular polymeric substances (EPS) in sludge hinder the efficient removal of sludge water due to their strong hydrophilicity and water-holding capacity. In this study, we prepared a new type of α-Mn2O3 by the hydrothermal method and explored the effects of α-Mn2O3/peroxymonosulfate (PMS) on the properties of EPS and sludge dewaterability. Results confirmed that centrifuged weight reduction (CWR) increased from 87.5 to 94.7%, while water content (WC) decreased from 78.1 to 70.4%, under optimized additions of α-Mn2O3 and PMS, which were 0.12 mmol/g VSS and 0.18 mmol/g VSS, respectively. The mechanism investigations indicated that α-Mn2O3/PMS clearly degraded the EPS, destroyed their structure, and weakened their hydrophilicity and water-holding capacity, leading to much reduced intermolecular forces of EPS and the transformation of bound water to free water. Furthermore, we also ascertained the oxidized mechanism of α-Mn2O3/PMS on the degradation of EPS, and the pathway for generating reactive oxygen species (ROS) was also uncovered. Remarkably, SO4•– and •OH were the leading ROS on the degradation of EPS during oxidation with beyond 70% rate of contribution. Importantly, prepared α-Mn2O3 was compared with the standard Mn2O3 to verify the feasibility of applying it in practical engineering applications. This research has great significance for applying persulfate to enhance sludge dewaterability, which is expected to promote the wide application of manganese oxides (MnOx)/PMS in sludge reduction and dewatering.

Determining the performance of lignin-based flocculants in improving biosludge dewaterability

In the wastewater treatment plant of pulp and paper mills, biosludge dewatering is needed to reduce the sludge handling and disposal costs. It is usually facilitated by means of the addition of synthetic polymers. There is increasing interest in replacing synthetic polymers with biopolymers derived from low value by-products or industrial residuals to improve the environmental footprint of dewatering. In this study, lignin-based flocculants (LBF) were tested for their ability to improve the biosludge dewaterability based on Capillary Suction Time (CST) and dry cake solids achieved with a Crown Press. The results demonstrate that LBFs alone can significantly enhance dewatering with a decrease in CSTs from 72.7 ± 5.1 s (unconditioned biosludge) to 23.3 ± 0.4 s and an increase in dry cake solids after pressing from 7.1 ± 0.5% to 13.9 ± 1.3% with a relatively high dosage of 7.5% w/w. However, with dual conditioning a LBF and 0.1% w/w anionic polyacrylamide (APAM), the required dosage of LBF was reduced to 3% w/w to achieve a dry cake solids content of 13.8 ± 0.4%, the same as that achieved with Zetag8165, a commercial synthetic polymer. LBF addition lowered the particle surface charge, allowing the particles to agglomerate and enhancing for the biosludge dewaterability. The application of LBFs for sludge dewatering offers novel considerable promise for providing more sustainable approaches by optimizing the use of lignin from different extraction processes, applying various types of lignin modifications in combination with anionic polymers, and exploring different methods of disposal or utilization of the dewatered sludge.

The Performance and Mechanism of Sludge Reduction by the Bioaugmentation Approach

Simple SummaryActivated sludge-based wastewater treatment process is one of the most popular adopted systems in wastewater treatment plants around the world. Excess sludge is an inevitable byproduct of the process, and the enormous quantity has brought a significant burden on operational costs. Various physicochemical and biological methods have been developed. Biological-based methods are promising because of less chemical consumption and low operation cost comparing to physicochemical methods. Hence, the present study is aimed at searching for functional bacteria that could reduce sludge, enhance the performance of sludge reduction through optimization, and try to unveil the underlying mechanism during sludge reduction. A total of 19 strains that belong to Firmicutes, Proteobacteria, and Actinobacteria were successfully isolated and identified. Subsequently, the performance of sludge reduction by pure culture or mix-cultures was validated. In total, 21.2% and 13.9% of total suspended and volatile suspended solids were reduced within 48 h after optimization via response surface methodology. The three-dimensional excitation-emission matrix fluorescence spectrum and hydrolases test results revealed that the sludge reduction might be promoted by the strain mainly through hydrolysis via proteinase and amylase. The results obtained from the study could help us to find an effective and economical way to resolve the sludge issue.Millions of wastewater treatment plants (WWTPs) based on the activated sludge process have been established worldwide to help to purify wastewater. However, a vast amount of sludge is inevitably generated, and the cost of sludge disposal could reach over half of the total operation cost of a WWTP. Various sludge reduction techniques have been developed, including physicochemical, biological, and combinational methods. Micro-organisms that could reduce sludge by cryptic growth are vital to the biological approach. Currently, only limited functional bacteria have been isolated, and the lack of knowledge on the underlying mechanism hinders the technique development. Therefore, the present study is aimed at isolating sludge-reducing bacteria and optimizing the sludge reduction process through response surface methodology. Nineteen strains were obtained from sludge. The mix-cultures did not show a higher sludge reduction rate than the pure culture, which may be ascribed to the complicated interactions, such as competition and antagonistic effects. In total, 21.2% and 13.9% of total suspended and volatile suspended solids were reduced within 48 h after optimization. The three-dimensional excitation-emission matrix fluorescence spectrum and hydrolases test results revealed that the sludge reduction might be promoted by the strain mainly through hydrolysis via proteinase and amylase. The results obtained from the study demonstrate the potential of using micro-organisms for sludge reduction through cryptic growth.

Optimum loading ratio for co-digested wastewater sludge and brewery spent yeast

Anaerobic digestion (AD) is one of the most widely used technologies in the world for converting solid organic waste into energy and other value-added products. In the treatment of municipal wastewater, the disposal of sewage sludge is a problem of growing importance, as it contributes significantly to the operating costs of a wastewater treatment plant. It has also been recognised as a pollutant, albeit one with energy potential. In the brewing industry, a significant proportion of the raw materials used also end up as secondary raw materials or waste. Due to increased energy prices, brewer’s yeast has attracted great interest as an energy substrate, despite its difficult degradability under anaerobic conditions. AD offers the possibility to produce biogas and digestate from sewage sludge, resulting in a reduction in sludge volume and disposal costs. However, mono-digestion of sewage sludge often yields only a small amount of biomethane. To improve the quality and quantity of biogas, co-digestion is often used, leading to an increase in the economics of AD. However, the feedstock and co-digestion ratio need to be understood and carefully selected because they can affect the optimal methane production. Therefore, this study investigates the proportion of co-substrate that can optimise biogas yield. The co-fermented samples with different loading ratios of 1:1, 1:2 and 2:1 were characterised in terms of C/N ratio, total solids (TS), volatile solids (VS), moisture content and pH. They were measured by the standard method. In addition, the methanogenic potential was determined based on the biomethane potential (BMP) using the AMPTS 11 test. From the study, it was found that the optimum co-fermentation ratio was 1:2 of WWS: BSY with the highest biomethane production of 338.2 NmL CH4/g VS. Consequently, it was found that co-digestion of WWS with BSY can improve biomethane production and that brewer’s waste yeast could mitigate some of the limitations associated with mono-digestion of sewage sludge.

A novel fuzzy framework for technology selection of sustainable wastewater treatment plants based on TODIM methodology in developing urban areas

Optimal technology selection of wastewater treatment plants (WWTPs) necessitates the adoption of data-driven scientific approaches that satisfy the sustainability requirements of the urban ecosystem. Such approaches should be able to provide actionable insights to decision makers constrained by factors such as population growth, land scarcity, and loss of functionality of wastewater treatment plants. The framework in this study proposes a hybrid fuzzy multi-criteria decision making (MCDM) model consisting of the analytical hierarchy process (AHP) and the TODIM (an acronym in Portuguese of interactive and multi-criteria decision-making) by using alpha cut series which takes into account the risk aversion of decision makers (DMs) to overcome uncertainties of environmental conditions. The literature to date indicates that the study is the first to presents how a systematic decision-making process is approached by interpreting the interaction of criteria for the selection of wastewater treatment technology through the membership function of Prospect Theory. The proposed methodology reveals that the prominent reference criterion manipulates other sub-criteria according to the function of risk-aversion behavior. The fuzzy sets based on alpha cut series are employed to evaluate both the criteria weight and the rank of the alternatives in the decision-making process to obtain compromise solutions under uncertainty. The dominance degrees of the alternatives are achieved by fuzzy TODIM integrated with the fuzzy analytic hierarchy process (FAHP) which deals with the uncertainty of human judgements. According to the ranking results determined by the dominance degree of alternatives, anaerobic–anoxic–oxic (A2O) without pre-clarification was the most effective process in relation to the sludge disposal cost (C25) calculated as reference criteria. The ranking of four full-scale WWTPs in a metropolitan city of an EMEA country based on 24 sub-criteria listed under the four main criteria, namely the dimensions of sustainability, is used as a case study to verify the usefulness of the fuzzy approach. Motivated by the literature gap related to the failure to consider the psychological behavior of DMs in technology selection problem for wastewater treatment, it is discussed how the proposed hybrid MCDM model can be utilized by reflecting human risk perception in wastewater treatment technology selection for developing urban areas.

Biosynthesis and recycling of magnetite nanocatalysts from Fe-rich sludge

Iron salts are widely used in municipal infrastructure to treat drinking water, prevent the corrosion of sewer lines and enhance phosphorus/nitrogen removal. The added iron salts deposit in sludge, leading to an increase in the cost of sludge disposal. Here, we demonstrated the feasibility of recycling magnetite nanoparticles (MNPs) produced from Fe-rich sludge under anaerobic conditions with indigenous microorganisms. The genus Geobacter was found to play the primary role in MNP synthesis. The produced MNPs were spherical with a size ranging from 12 to 24 nm. Compared to commercialized MNPs, the extracellular polysaccharides protected their surficial Fe2+ from being oxidized. The biosynthesized MNPs had a catalytic performance similar to that of commercialized MNPs but with high reusability after multiple cycles. These results demonstrate that the biosynthesis of MNPs is a novel and applicable way to recycle value-added products from Fe-rich sludge.

Developing a novel gasification-based sludge-to-methanol utilization process and exergy-economic-environmental (3E) analysis

Sewage sludge is a common waste from wastewater treatment plants in Hong Kong and conventional treatment ways like the landfilling method has been gradually abandoned considering the environmental impacts and costly land. Searching for integrating processes to well treat the sludge simultaneously achieve the energy recovery can be a good alternative way. Therefore, process design and simulation of a gasification-based sludge to methanol (STM) production was proposed in this work. It considered major subsections such as gasification, power generation, absorption, methanol synthesis, and distillation. Followed by the sensitivity analysis to optimize operational parameters, economic, environmental, and exergy (3E) analysis of STM process was conducted. The economic estimation revealed the methanol production cost is 579.62$/ton and the sludge disposal cost is 39.58$/ton. The calculated internal rate of return (IRR) of the process is 10.20% and 5.48%, respectively with a subsidy of 20$/ton sludge and without any support. Moreover, it was found the greenhouse gas (GHG) emission was 3.21 kg eq.CO2/kg methanol and overall exergy efficiency was 37.92%. The current work implies the great potential of STM treatment strategy, which can serve as a reference for the future sludge treatment planning.

Combining Shift to Biogas Production in a Large WWTP in China with Optimisation of Nitrogen Removal

Despite the huge current challenges in sewage sludge treatment and disposal in China, anaerobic sludge stabilisation (AnSS) is still not a state-of-the-art process in WWTP in the country. However, the potential benefits of anaerobic sludge stabilisation may outweigh the drawbacks. One of these drawbacks is the backload from the sludge liquor that increases the nutrient load in the biological treatment stage. This work shows via computer modelling that not only can the sludge production and disposal costs be significantly reduced, but also that, with sensible automation and operational strategies (e.g., bypass of primary clarifiers, use of a centrate dosing strategy, incorporation of ammonium nitrogen sensors, etc.), the effects of the backload can be counteracted for nitrogen removal, even considering that wastewater in China often has an unfavourable C/N ratio for nitrogen removal. The tested strategies would even improve the overall plant performance in terms of norm compliance, sludge production, energy use, and energy production

Analysis of the variation of costs for sewage sludge transport, recovery and disposal in Northern Italy: a recent survey (2015-2021).

The cost for the recovery/disposal of residues produced by wastewater treatment plants (WWTPs) represents a relevant aspect in the economics of WWTP management. We elaborated and applied a desk-based methodology to analyze tender processes and to investigate quantitatively and qualitatively the variability of unit costs for sewage sludge (EWC 190805) management in Northern Italy from 2015 to 2021. We conducted a qualitative survey for operators of the sector. Unit costs for sludge management increased over time. The unit cost was mostly affected by the type of sludge recovery/disposal being the cost for recovery in agriculture (direct or by composting) lower than incineration and landfilling. Other variables influencing the cost were the distance and discount offered by the contractor. Regulatory and judiciary events determined a sudden increase of sludge disposal costs in Italy between 2017 and 2019. Recovery in agriculture, when practicable, remains the preferable option. Results can orient and support the optimization of sludge management costs and be of interest for future studies at national or European level.

Application of cerium and lanthanum coagulants in wastewater treatment—A comparative assessment to magnesium, aluminum, and iron coagulants

Biological wastewater treatment plays a central role in removing nutrients from wastewater. However, during the dewatering of biological sludge before it is transported to a landfill, a concentrated stream (centrate), loaded with phosphate, nitrogen, organic matter, and suspended solids, among others, is formed. Recycling these elevated concentrations, especially soluble phosphorus, back to the head of the plant defeats the sole purpose of enhanced biological treatment. In this study, a centrate stream was treated with lanthanides through coagulation. The study also established comparative performance between lanthanides and other commonly used coagulants, like FeCl3, Al2(SO4)3, Na2Al2O4, and Mg(OH)2. Coagulant performance was assessed based on their capacity to remove dissolved phosphorus and other impurities while maintaining alkalinity, sludge production, and operation cost. While adjusting the pH of the centrate (4.0–9.0), Al2(SO4)3, FeCl3, Na2Al2O4, LaCl3, and CeCl3 demonstrated strong removal of phosphate (>50%) at pH ≥ 6.0. However, as the pH dropped (≤5.0), the performance of both alum and FeCl3 plummeted to less than 15%. Na2Al2O4, CeCl3, and LaCl3 coagulants are not affected by pH; they maintained at least 85% phosphate precipitation at all tested pH values. The trend for moles of metal ion to phosphorus ratio required to treat centrate is as follows CeCl3 [1.2] = LaCl3 [1.2] < FeCl3 [1.5] < Na2Al2O4 [1.8] < alum [2.5] < Mg(OH)2 [3.1]. Evaluating each coagulant's performance based on purchase price, sludge disposal cost, and alkaline/acid reagent cost, Mg(OH)2 coagulant is the least expensive to treat wastewater in the given case study. However, based on effluent water quality, lanthanides outperform all the tested coagulants. Assessment of the lanthanide precipitates reveals that there is direct bonding between lanthanide and phosphate.

Operation and maintenance financial feasibility analysis of centralized domestic wastewater treatment system (case study: Palembang City Sewerage Project)

Budget needed for operation and maintenance of centralized domestic wastewater management in Indonesia is often overlooked. This results in fail systems, high idle capacity, and abandoned assets. While the economic feasibility often used as the basis for centralized domestic wastewater infrastructure construction, the financial feasibility often shown a different result. The construction phase will be feasible according the analysis, while the operation and maintenance phase will have a different result. As unsolicited projects, the operation and maintenance of sewerage in Indonesia always have budget difficulties, thus needed scenario to resolve the matter. In this study, cost and revenue variable will be analyzed to determine the feasibility value based on NPV, BCR, and IRR calculations. The revenue comes from user charge tariffs on household and commercials connections, and cost variable consists of: chemical usage cost; sludge disposal cost; personnel wage cost; fuel and electricity cost; spare-part replacement cost. The analysis will determine whether both household connection and commercials connection in the sewerage system have positive results. Should negative results emerged, follow up analysis added to elevate the results consists of following scenarios: sensitivity analysis for tariffs adjustment; sensitivity analysis adding grant as option; sensitivity analysis adding loan as option. While analysis of base tariffs shown negative results on NPV, BCR, and IRR calculation, the follow up analysis shown significant changes thus the results is desirable.

Techno-economic evaluation of ozone-oxidation for sludge reduction at the full-scale. Comparison between the application to the return activated sludge (RAS) and the sludge digestion unit

Ozone oxidation was applied to a fraction (30 %) of the return activated sludge (RAS) of a full-scale Wastewater Treatment Plant for reducing the high sludge production (20 t/week). The amount of sludge sent to final disposal was decreased by 50 % and 75 % at 0.55 kgO3/h and 0.80 kgO3/h dosage, respectively. When the same ozonation system was applied to the aerobic digestion (0.06, 0.50, 0.67 kgO3/h), the reduction was 27–77 %.A thorough economic analysis was carried out considering the overall sludge quantity finally extracted from the plant in the presence and absence of ozonation, the corresponding costs of final disposal and the ozone oxidation operation costs. The net cost saving for sludge disposal was calculated to be 66.6 €/d and 109.9 €/d due to ozone in the return activated sludge at the two dosages, respectively. When ozonation was applied to the recycled sludge of the digestion unit, the net cost saving was in the range 235–655 €/d, depending on the reduction percentage achieved. The ozone oxidation showed to become economically convenient for a sludge disposal cost lower than that sustained by the Company. The results obtained prove feasibility of ozonation for sludge reduction in both locations of the WWTP: therefore, with respect to other disintegration techniques, ozonation possesses a high technical and economic advantage along with a high versatility. Furthermore, it is also shown the feasibility of lowering the applied dosages with respect to the past experiences, since effectiveness of the system is still guaranteed.