Sludge Line Research Articles

Evaluation of the energy efficiency of a large wastewater treatment plant in Italy

Energy consumption represents a significant part of the operative costs of a wastewater treatment plant but, with a correct design and a careful management model, there are important possibilities for its limitation. The proposed research presents a multi-step methodology for the evaluation of the energetic aspects of wastewater treatment, which was implemented on the largest facility in Italy (2.7M population equivalents as organic load), managed by Società Metropolitana Acque Torino (SMAT). The study initially took into account each phase of the process scheme, in order to obtain specific electricity consumption values for all the electro-mechanic devices. Data from tele-control system and direct measurements in field have both been acquired. The total electric energy demand of the plant was evaluated (66.78GWh/y, about 50% from aeration in oxidation tanks). In account of large contribution the energy efficiency of the blowers was verified with positive results. Four specific energy consumption indexes were considered to carry out a critical analysis of SMAT wastewater treatment plant with other facilities performing biological oxidation processes and of a different order of magnitude about design capacity, and congruent values were obtained. The considered indexes related the electric energy demand to the equivalent population, to the volume of treated water and to the amount of removed COD and total Nitrogen. Furthermore the thermal energy demand of the plant was estimated (49.15GWh/y, more than 93% from sludge line). An energy balance for the whole plant was finally evaluated, and some energy optimization solutions to decrease the corresponding costs were suggested.

Two advanced biological approaches for sludge minimization from municipal wastewater treatment

Two advanced biological solutions for sludge minimization in wastewater treatment are tested. The first solution, particularly suitable for new installations, is based on the application of the sequential batch biofilter granular reactor (SBBGR). The second one, mostly appropriate for existing plants, is the alternate cycles process applied in the sludge line (ACSL) of conventional activated sludge systems. The results of treating raw municipal wastewater show that the SBBGR system is able to reduce the quantity of sludge up to 80%. Furthermore, the produced excess sludge requires no longer stabilization compared with the usual aerobic/anaerobic one. As regards the ACSL process, the results obtained in the full scale have shown an observed sludge yield reduction up to 54% with an increase in the specific oxygen uptake rate up to 20 mgO2/gVSS/h. Finally, applying the ACSL process low specific consumption of energy is required.

Case study of Marquette-Lez-Lille WWTP: application of IFAS and THP for a city of the future

The Lille metropolitan area awarded Veolia Water the contract to reconstruct the Marquette-lez-Lille wastewater treatment plant (WWTP) in 2010, the biggest such facility in the north of France. The capacity of the new WWTP is 700,000 m³/day, serving a population of 620,000. It will be built on the site of the previous one, which is now obsolete. The renovation work comprises four treatment lines, including wastewater, stormwater sludge treatment lines, and a deodorization line. By applying state-of-the-art design and proven technologies, especially Hybas™ and Exelys™-DLD, a sustainable development solution was provided to local communities. The effluent from the new plant will meet the requirements of the European Water Framework Directive (Directive 2000/60/EC) on ‘good ecological status’ of water, and the treated storm water will be used to irrigate 7 hectares wetland. Compared with conventional digestion, the Exelys™-DLD configuration will further reduce sludge quantities by 30% and increase biogas production by 20%. Thereby, 94% of the power requirements will be supplied from the plant itself. The water line started operating in February 2013, and commissioning of the sludge line, which started in July 2014, was expected to finish in February 2015. In this paper, the design concept of the sustainable development solution is presented, as well as the application of showcase technologies for wastewater and sludge treatment.

Full-scale phosphorus recovery from digested waste water sludge in Belgium - part I: technical achievements and challenges.

To date, phosphorus recovery as struvite in wastewater treatment plants has been mainly implemented on water phases resulting from dewatering processes of the sludge line. However, it is possible to recover struvite directly from sludge phases. Besides minimising the return loads of phosphorus from the sludge line to the water line, placing such a process within the sludge line is claimed to offer advantages such as a higher recovery potential, enhanced dewaterability of the treated sludge, and reduced speed of scaling in pipes and dewatering devices. In the wastewater treatment plant at Leuven (Belgium), a full-scale struvite recovery process from digested sludge has been tested for 1 year. Several monitoring campaigns and experiments provided indications of the efficiency of the process for recovery. The load of phosphorus from the sludge line returning to the water line as centrate accounted for 15% of the P-load of the plant in the reference situation. Data indicated that the process divides this phosphorus load by two. An improved dewaterability of 1.5% of dry solids content was achieved, provided a proper tuning of the installation. Quality analyses showed that the formed struvite was quite pure.

Sludge Treatment Analysis in Potable Water Treatment Plant (PWTP) in Logroño (Spain)

In a Drinking Water Plant the first step in purifying water is the removal of the suspended solids and other organic or inorganic compounds (silts, clays and very fine particles). The separation is based on settling processes that is carried out through coagulation and sand filtration and the resultant product in the process is sent to sludge line. In this line, the sludge is flocculated, decanted and then thickened. As the water obtained is recirculated to first-stage treatment, the concentrated sludge is dehydrated for later use. The sludge contains a large amount of flocculants and as a result, the sludge recirculation would be possible so as to reduce the dosages of the chemical polymer streamlining the process of dehydration. This study shows the inefficiency of the sludge recirculation, and therefore proposes sludge removal process for future designs and sludge lines projects.

Activated sludge with low solids production: modified ASM1 modeling and simulation

Dynamic activated sludge modeling (ASM) and the concept of chemical oxygen demand fractionation utilized by this modeling approach suggested the existence of new strategies for minimization of excess sludge. One of these strategies consists of eliminating the traditional sludge wastage (WAS) and avoiding the buildup of inert solids in the aeration tanks by other means: fine screens are used to remove the inert particulate organic fraction (XI), hydrocyclones (HC) are used for inorganic suspended solids (ISS), and different types of online digesters are used to further biodegrade the endogenous residues (XP) via the return activated sludge (RAS) line. In this research, a model and a simulation program were developed that were able to mimic the apparent behavior of activated sludge variants with low solids production (LSP-AS). The model is an extended ASM1 assuming a small first-order biodegradation constant for XP(kXp = 0.007 d−1), and black boxes represent XI and ISS removal. The simulations first depicted the way that different solid components build up in the aeration tanks when traditional activated sludge (C-AS) is operated at very high solids retention times (>100 d, without sieves and HC). Secondly, the modeling showed that the C-AS process could hypothetically be replaced by LSP-AS variants with similar levels of active biomass and mixed liquor total suspended solids in the aeration tanks (2,500–3,500 mg L−1 TSS). For the studied case, at least 2 and 6% of the RAS flow must be screened and digested, respectively, to avoid the accumulation of XI, ISS, and XP. Additionally, the size of the online digester will be approximately twice the volume of the aeration tank. The mathematical model implemented in Aquasim could serve as a didactical, operational, and research simulation tool for LSP activated sludge processes.

Reduction of the excess sludge production by biological alternating process: real application results and metabolic uncoupling mechanism

The biological solution proposed to reduce the wasted sludge production is based on a process of alternating phases realized in a specific reactor (alternate cycles in sludge line (ACSL)) where a quote of the recycle sludge is treated and sent back to the main activated sludge process. The ACSL process was applied in two urban wastewater treatment plants (WWTPs). The reduction was tested by changing the hydraulic retention time and the conditions of oxidation reduction potential. The main mechanism of the process is recognized in the metabolic uncoupling. In fact, an increase in the specific oxygen uptake rate in the biological reactors was recorded (up to 20 mg/g VSS/h), which was stimulated by the fasting condition in the ACSL. The process is able to reduce the observed sludge yield on average of 25–30% with final average values reaching 0.179 kg VSS/kg chemical oxygen demand (COD) for WWTP1 and 0.117 kg VSS/kg COD for WWTP2.

Study on the Treatment of Excess Activated Sludge on the Return Sludge Line

The motion of ferrite particles was used to treat the excess activated sludge produced in waste water treatment plants. The motion of ferrite particles was controlled by two electromagnets (EMs). We have proposed a magnetic circuit with two metal plates between the EMs, so that the magnetic flux of the magnets can be obtained for a larger area. Thus, a larger container with activated sludge can be treated and by applying an AC voltage to it, can be sterilized and its quantity can be reduced. Our experiments show the prospects of using magneto-ferrite treatment in the return line of activated sludge in a sewerage plant.

Implications of full-scale implementation of an anammox-based process as post-treatment of a municipal anaerobic sludge digester operated with co-digestion

The feasibility of treating the supernatant of a municipal sludge digester supplemented with co-substrates by means of an anammox-based process (ELAN(®)) was tested in Guillarei (NW of Spain). Ammonia concentration measured in the supernatant of the sludge digester varied in the range 800-1,500 g N/m(3) due to the fact that the sludge produced in the plant was co-digested with wastes coming from surrounding food industries. Treating this supernatant in the ELAN(®) reactor, nitrogen removal rates up to 1.1 kg N/(m(3) d) were reached in experiments run in a pilot plant reactor operated in batch mode. No nitrite oxidation was registered after several months of operation despite the average dissolved oxygen (DO) concentrations being 1.5 g O2/m(3) and the temperature reaching values as low as 18 °C. By keeping the DO set point at 1-2 g O2/m(3) and tuning the hydraulic retention time, the stability of the process was guaranteed and the presence of co-substrates in the anaerobic digester did not affect negatively the operation of the autotrophic nitrogen removal process. Due to the success of the pilot plant experiment, an upscale of the process to full scale is proposed. Mass balances applied to Guillarei wastewater treatment plant revealed that in the main stream line the average denitrification rate calculated with the data of year 2011 was 226 kg N/d. Since the nitrogen removal efficiency is limited by the amount of readily biodegradable organic matter available to carry out denitrification in the water line, the implementation of an anammox-based process to treat the supernatant seems the best option to improve the effluent quality in terms of nitrogen content. The nitrogen removal rate in the sludge line would be 30 times higher than the one in the water line. The implementation of the process would improve the energetic balance and the nitrogen removal performance of the plant.

Treatment of waste activated sludge together with agro-waste by anaerobic digestion: focus on effluent quality

Waste activated sludge production and management plays an important role in wastewater treatment plants (WWTPs), especially from an economic point of view. One possible approach is the anaerobic co-digestion of waste activated sludge with others organic substrates in mesophilic and thermophilic conditions in order to exploit the spare volume of existing reactors, recover energy from biogas production, and obtain a fertilizer as final product. The anaerobic trials were carried out at pilot scale, applying two organic loading rates (2.8 and 4.5 kg chemical oxygen demand (COD)/(m(3)·d)) with a hydraulic retention time of 16 and 21 days. Among agro-wastes, wine lees were chosen because of their continuous availability throughout the year, and their high COD content (up to 200-300 g/l, 70% soluble, on average). The addition of wine lees to activated sludge determined a higher biogas production (best yield was 0.40 Nm(3)/kgCOD(fed)) improving the energetic balance of the sludge line of the WWTP. The characterization of both substrates fed and digester effluents was carried out in terms of heavy metals; comparison with EC proposed limits showed that, due to high content of Cu in wine lees, the loading rate of this agro-waste should be limited to maintain good characteristics of final biosolids.

Lab-scale optimization of propylene glycol removal from synthetic wastewater using activated sludge reactor

ABSTRACTPropylene glycol (PG) is not a toxic matter. However, it can dramatically increase BOD of water resources and that is why removal of PG is important. Removal of PG in synthetic wastewater was studied in a continuous activated sludge pilot-scale reactor. The influence of various factors (pH, nitrogen source, COD and wastewater feed salinity (conductivity)) on micro-organism growth as a measure of removal was determined, and the optimum condition for maximizing this response was obtained using Taguchi experimental design method. Primary micro-organisms were obtained from the return sludge line of the Shahrak-Gharb wastewater treatment system located in the city of Tehran. The micro-organisms have been adapted to high organic loads during five stages in 119 days. The maximum PG removal efficiency was equal to 85%. In the selected range of levels, the best pH was equal to 8 and the influent COD was 1300 mg/L. The best nitrogen source was urea, and salinity was obtained equal to 8%.

Plant-wide modelling and simulation using steady-state data: a case study of the Gliwice WWTP, Poland

In last decade the focal point of the activated sludge (AS) modelling shifted from a secondary-treatment to a plant-wide level. This new approach offers more possibilities, therefore demands more effort and expertise from a modeller. This paper presents a plant-wide approach to modelling and simulation of a full-scale AS wastewater treatment plant (WWTP). The construction and routine operational data of the full-scale Central WWTP in Gliwice (Poland) were used in this study to develop an integrated model of the water and sludge lines of the plant. The core of the plant model was the Activated Sludge Model No.1 (ASM1), which combined with sub-models of the other processes, was implemented in the WEST® Software version 3.7.6. The calibration strategy, verification and predictive capacity of the model are discussed. The calibrated model permitted acceptable accuracy of the simulation, yet limited data restrained its scope. Thus, the obtained mathematical description of the plant is a preliminary yet sound basis for a more versatile model. The model limitations and opportunities for its further applications and development are discussed.

Environmental profile of typical anaerobic/anoxic/oxic wastewater treatment systems meeting increasingly stringent treatment standards from a life cycle perspective

Stringent new legislation for wastewater treatment plants (WWTPs) is currently motivating innovation and optimization of wastewater treatment technologies. Evaluating the environmental performance of a wastewater treatment system is a necessary precursor before proposing implementation of WWTPs designed to address the global requirements for reduced resource use, energy consumption and environmental emissions. However, developing overly-sophisticated treatment methods may lead to negative environmental effects. This study was conducted to employ a process modeling approach from a life cycle perspective to construct and evaluate six anaerobic/anoxic/oxic wastewater treatment systems that include a water line, sludge line and bioenergy recovery system and was designed to meet different treatment standards in China. The results revealed that improved treatments optimized for local receiving watercourses can be realized at the cost of higher resource consumption and greenhouse gas emissions. Optimal Scenarios were also identified from different positive perspectives.

Comparison between ozonation and the OSA process: analysis of excess sludge reduction and biomass activity in two different pilot plants

The excess biomass produced during biological treatment of municipal wastewater represents a major issue worldwide, as its disposal implies environmental, economic and social impacts. Therefore, there has been a growing interest in developing technologies to reduce sludge production. The main proposed strategies can be categorized according to the place inside the wastewater treatment plant (WWTP) where the reduction takes place. In particular, sludge minimization can be achieved in the wastewater line as well as in the sludge line. This paper presents the results of two pilot scale systems, to evaluate their feasibility for sludge reduction and to understand their effect on biomass activity: (1) a pilot plant with an ozone contactor in the return activated sludge (RAS) stream for the exposition of sludge to a low ozone dosage; and (2) an oxic-settling-anaerobic (OSA) process with high retention time in the anaerobic sludge holding tank have been studied. The results showed that both technologies enabled significant excess sludge reduction but produced a slight decrease of biomass respiratory activity.

Advanced Thermal Hydrolysis: Optimization of a Novel Thermochemical Process to Aid Sewage Sludge Treatment

The aim of this work was to study in depth the behavior and optimization of a novel process, called advanced thermal hydrolysis (ATH), to determine its utility as a pretreatment (sludge solubilization) or postreatment (organic matter removal) for anaerobic digestion (AD) in the sludge line of wastewater treatment plants (WWTPs). ATH is based on a thermal hydrolysis (TH) process plus hydrogen peroxide (H(2)O(2)) addition and takes advantage of a peroxidation/direct steam injection synergistic effect. On the basis of the response surface methodology (RSM) and a modified Doehlert design, an empirical second-order polynomial model was developed for the total yield of: (a) disintegration degree [DD (%)] (solubilization), (b) filtration constant [F(c) (cm(2)/min)] (dewaterability), and (c) organic matter removal (%). The variables considered were operation time (t), temperature reached after initial heating (T), and oxidant coefficient (n = oxygen(supplied)/oxygen(stoichiometric)). As the model predicts, in the case of the ATH process with high levels of oxidant, it is possible to achieve an organic matter removal of up to 92%, but the conditions required are prohibitive on an industrial scale. ATH operated at optimal conditions (oxygen amount 30% of stoichiometric, 115 °C and 24 min) gave promising results as a pretreatment, with similar solubilization and markedly better dewaterability levels in comparison to those obtained with TH at 170 °C. The empirical validation of the model was satisfactory.

Excess sludge reduction by biological way: From experimental experience to a real full scale application

The aim of this study was to investigate the ability of a biological process applied in the sludge line and based on the alternation of oxic and anoxic phases, to minimize the waste sludge production. After some tests in pilot scale, the process was applied in a real municipal wastewater treatment plant of 35,000PE trying out one setting of working experimental conditions. A rate of the recycle flow was conditioned in a treatment basin, maintaining an HRT of 10days. The control device operated for the 50% of time in the ORP range between −400 and −200mV, and for the 50% in the ORP range between −200 and +50mV. The mass balance defined an actual observed growth yield equal to 0.09kgTVSkgCODr-1, and the heterotrophic yield values, assessed by batch tests, seemed to be a suitable marker for the sludge reduction and for the energy uncoupling.

Life Cycle Assessment of an intensive sewage treatment plant in Barcelona (Spain) with focus on energy aspects

Life Cycle Assessment was used to evaluate environmental impacts associated to a full-scale wastewater treatment plant (WWTP) in Barcelona Metropolitan Area, with a treatment capacity of 2 million population equivalent, focussing on energy aspects and resources consumption. The wastewater line includes conventional pre-treatment, primary settler, activated sludge with nitrogen removal, and tertiary treatment; and the sludge line consists of thickening, anaerobic digestion, cogeneration, dewatering and thermal drying. Real site data were preferably included in the inventory. Environmental impacts of the resulting impact categories were determined by the CLM 2 baseline method. According to the results, the combustion of natural gas in the cogeneration engine is responsible for the main impact on Climate Change and Depletion of Abiotic Resources, while the combustion of biogas in the cogeneration unit accounts for a minor part. The results suggest that the environmental performance of the WWTP would be enhanced by increasing biogas production through improved anaerobic digestion of sewage sludge.

Comparison of Aerobic and Lime Stabilization Methods for Evaluation of Sewage Sludge Reuse

The main objective of this research was the examination of effectiveness of lime dose in order to stabilization of sewage sludge and comparison of lime stabilized sludge reuse with aerobic digested sludge reuse. Lime and aerobic stabilization were carried out in two laboratory reactor with 40 L capacity. The sludge samples were taken from the return activated sludge line in four times. Lime was used at various ratios and the mixture was stabilized for 30 days. During the lime hydrated stabilization pH values were significantly increased from 7 to 12.5. Also, aerobic digester was loaded with raw sludge and mixed by sufficient amount of air for 30 days. The results indicate that the lime addition with the dose of 0.4 g Ca(OH)2 g-1 DS could completely inactive a high amount of fecal coliforms within 1 h and in all of the times was lower than 1000 MPN g-1 DS after 30 days (p<0.01). But after 30 days, fecal coliforms density in aerobic digested sludge could not achieve to Class A of USEPA category. In two stabilization methods, density of viable helminths ova could not reduce to 1 ova/4 g DS and could not achieve to Class A of USEPA category. Therefore, these methods could be achieved the reduction requirement set by USEPA for class B (p<0.01) and the products could be well used as a landfill cover or a soil conditioner. Finally, our study confirmed that lime sludge stabilization has a higher hygienic effect and more cost-effective than aerobic stabilization, specially, when such sludge is used to dung and modify acid soils.© 2011 Asian Network For Scientific Information.

Evolution of organic matter in a full-scale composting plant for the treatment of sewage sludge and biowaste by respiration techniques and pyrolysis-GC/MS

A full-scale composting plant treating in two parallel lines sewage sludge and the source-selected organic fraction of municipal solid waste (OFMSW or biowaste) has been completely monitored. Chemical routine analysis proved not to be suitable for an adequate plant monitoring in terms of stabilization and characterization of the process and final compost properties. However, the dynamic respiration index demonstrated to be the most feasible tool to determine the progression of the degradation and stabilization of organic matter for both sewage sludge and OFMSW lines. Both lines exhibited an important degree of stabilization of organic matter using rapid and cumulative respiration indices. Pyrolysis-GC/MS was applied to the most important inputs, outputs, and intermediate points of the plant. It proved to be a powerful tool for the qualitative characterization of molecular composition of organic matter present in solid samples. A full characterization of the samples considered is also presented.

WORK OF COMBINED LARGE DIAMETER PIPE (SLURRY PIPELINE) ON ALLUVIAL SOILS TAILING HGF

The research results of influence of the deformation of tailing-dump dams on the sludge lines are considered. In designing the routes of sludge lines, it is offered to calculate the base deformations under the sludge line to substantiate the anti-destruction protection of sludge lines.