Sludge Disposal Costs Research Articles

Bench- and pilot-scale sludge electrodewatering in a diaphragm filter press

Electrodewatering is a technique in which pressure dewatering is combined with electrokinetic effects to realize an improved solid/liquid separation and hence increased filter cake dry matter contents. In order to be energy efficient, it is shown that sludge should be dewatered by pressure dewatering to a high extent prior to electric field application, and a sufficient contact time for the electric field must be guaranteed. In order to realize these goals, a bench- and pilot-scale diaphragm filter press suited for electrodewatering were constructed for treatment of sewage and other types of sludges. It was shown that electrodewatering of sludge is a feasible technique, especially for biological sludge types. Other types of sludge are less suited for electrodewatering because of the restricted improvements that can be realized in cake dry matter content and the high electric energy consumption. Furthermore, it was shown in pilot-scale tests that the use of a diaphragm filter press with electrodewatering facilities was very well suited to deliver dry filter cakes of sewage sludge at a moderate energy consumption. Depending on local market prices for investment, operating and sludge disposal costs, this technology may therefore lead to important savings in the sludge management process.

Comparison of Submerged Membrane Bioreactor in Different SRT Conditions

Complete sludge retention MBR appears to be an innovative technology which no sludge will be produced, hence eliminating the sludge disposal cost. However, the understanding of microbial behaviour in the complete sludge retention MBR was still not adequately established. This study was conducted to investigate the biological performances and microbial behaviour of three different SRT MBRs (5 days SRT, 10 days SRT and prolonged SRT). The results revealed that membrane filtration assisted for maintaining the high degree of organic removal (above 97%) for all MBRs. High organic degradation was noticed in the prolonged SRT MBR (89.44%) compared with 5 days SRT (77.64%) and 10 days SRT (85.62%) MBRs. This showed that the prolonged SRT MBR posed a greater capability for further degradation of inert organics and SMP. Extremely low sludge yield (0.0388 g VSS/g COD) was occurred in the prolonged SRT condition compared with 5 and 10 days SRT conditions. The low SOUR did not affect the degradation performance. Whereas, it implied that small amount of oxygen was sufficient to achieve high degree of organic degradation during the prolonged SRT MBR condition.

Development of MBR with reduced operational and maintenance costs

To reduce MBR O&M costs, a new MBR process that conducts efficient simultaneous biological nitrogen and phosphorus removal (BNR) was developed. In the development of this process, various approaches were taken, including reduction of power demand, chemical consumption and sludge disposal costs. To address power demand reductions, air supply requirements for membrane cleaning were reduced. The process adopted an improved membrane that requires less air for cleaning than conventional membranes. It also introduced cyclic aeration, which alternately supplies washing air to the two series of membrane units. Adoption of biological phosphorus removal eliminated chemical costs for phosphorus removal and contributed to the reduction of sludge disposal costs. By combining these technologies, compared to conventional MBR processes, an approximately 27% reduction in O&M costs was achieved.

Comparative economic analysis of the impacts of mean cell retention time and denitrification on aeration systems

Biological nutrient removal is practiced in various modifications of the activated sludge process (ASP) throughout the world. This paper compares conventional, nitrifying-only and combined nitrifying/denitrifying (NDN) processes. The authors performed 113 oxygen transfer efficiency measurements with the off-gas method over 20 years. This dataset was analysed and used to perform an economic analysis for three example scenarios, one for each layout (conventional, nitrifying-only and NDN). Field oxygen transfer efficiency and relevant plant operative costs and credits were considered (i.e., aeration cost, sludge disposal cost, methane production credit). The conclusion is that NDN operations always have lower aeration costs, and generally have the lowest combined operating cost. Reduced aeration costs result because of improved aeration efficiency at higher mean cell retention times and the use of nitrate as an electron acceptor. The improved aeration efficiency overcomes the increased oxygen required at higher cell retention time due to cell decay.

Sludge Dewatering and Disposal Practices for Small Activated Sludge Wastewater Treatment Plants

Sludge dewatering is a decisive step in the reduction of waste sludge volume, thus considerably affecting total sludge treatment and disposal costs. The construction of sludge dewatering facilities in small WwTPs though, is generally not cost effective. In this paper some experimental evidence is presented, that waste sludge dewatering in small WwTPs of the activated sludge—extended aeration type, can be effectively achieved by a centrifuge type of equipment withdrawing sludge directly from the aeration tank; an economic evaluation of the possibility to employ a transportable type of similar equipment mounted on a truck, to serve a number of small WwTPs located in remote or isolated areas is also presented and discussed.

EVALUATION OF SLUDGE PRODUCED BY LIMESTONE NEUTRALIZATION OF AMD AT THE FRIENDSHIP HILL NATIONAL HISTORIC SITE

A pulsed limestone bed (PLB) treatment plant for remediation of acid mine drainage (AMD) has been tested at the Friendship Hill National Historic site in southwestern Pennsylvania. The plant performed well, neutralizing over 50 metric tons of acidity over a 14-month period, but the cost of disposal of the 450 metric tons of sludge generated was high, because the sludge was hauled from the site and disposed of in a commercial landfill to minimize the impact on park property. Although the sludge was found to be non-hazardous based on the Toxicity Characteristics Leaching Protocol (TCLP), hauling and disposal costs were still elevated, at $40 per m 3 . Since sludge handling and disposal was a significant fraction of the operating cost of the facility, a study of the sludge characteristics and possible alternate handling methods was undertaken. Samples of AMD influent, treated water and settled sludge were used in a series of small- scale treatment studies. These tests showed that the sludge volume produced by limestone neutralization was less than half of that for lime, sodium hydroxide or ammonia. The settling rate was also greater for the limestone-based sludge. Vacuum filtration tests demonstrated that the limestone sludge was more readily filtered than sludges generated with sodium hydroxide or lime and that solids contents of up to 28% could be achieved. Because of lower maintenance costs, pressure filtration using a plate and frame filter is recommended for future plant operations. In this case, solids contents of as high as 31% were realized. As an alternative to the operating costs of mechanical filtration, a settling/percolation process was tested. Percolation tests showed that solids content of the settled sludge could be increased from 8% to 25%. These results show that sludge disposal costs for the treatment plant could be decreased through installation of a settling or filtration process. Moreover, the PLB process offers saving not only in reagent costs, but also in sludge disposal costs, through decreased sludge volume generated, rapid settling rates and ready filterability.

Water‐Treatment Works’Sludge Management

AbstractIn the UK, the disposal of wastes from the production of potable water has been an increasing problem for water companies since the introduction of the Waste Management Licensing Regulations in 1994. This paper considers alternative management strategies. The importance of investigating each works individually is stressed because of variations in sludge properties and disposal costs. Of the disposal options, the growing of turf is environmentally sustainable and economically attractive, whereas direct spreading on agricultural land and use in soil production can be successful. Other uses, e.g. in ceramics, are at various stages of development; co‐disposal with sewage is an option, but hidden costs need to be assessed.

A factorially‐designed study of physicochemical reactive dye colour removal from simulated cotton textile processing wastewaters

The process performance of coagulation to remove reactive dyes from dyehouse effluent is affected by multiple factors, which can be best examined in factorially‐designed experiments. A preliminary jar‐test procedure was used to select coagulants and the optimal pH and coagulant dosage ranges. An inorganic salt (ferrous sulphate) and an organic polymer (DEC 50) were selected for further studies. Factorially‐designed jar‐test experiments were performed with different compositions of a synthetic cotton processing wastewater to determine which factors most affected colour removal and highlight interactions between them. Some additives, such as an oxidative desizing agent and a peroxide stabiliser, favoured colour removal within specific concentration ranges. The presence of sizing agents and surfactants reduced process efficiency. Increasing concentrations of ferrous sulphate could counteract this, but would result in higher sludge disposal costs.

Thermophilic anaerobic digestion and pasteurisation. Practical experience from Danish wastewater treatment plants

Increasing sludge disposal costs have highly intensified the interest in reducing the sludge quantities from Danish wastewater treatment plants. By upgrading existing mesophilic digesters to the thermophilic temperature range, the retention time can be halved and many digesters designed only for primary sludge will have sufficient capacity to treat also the biological excess sludge. At the moment, eight full-scale thermophilic digesters are in operation in Denmark and five are under construction. This paper describes the full-scale experience gained from digestion of biological excess sludge as well as a mixture of primary and biological sludge. Thermophilic digestion has proven to be a good and stable process for solids reduction and pathogen removal. The digested sludge can be dewatered to a high solids content and thereby the sludge quantity for disposal can be reduced by 30-40% depending on the type of wastewater treatment plant. A drawback of the process is that the polymer costs for sludge dewatering may be increased depending on the sludge type.

Pilot-Scale Investigation of Chemical Addition-Dissolved Air Flotation for the Treatment of an Oily Wastewater

An investigation at the pilot scale of chemical addition-dissolved air flotation (CA-DAF) treatment of an oily wastewater was carried out comparing two chemical addition schemes [Grace Dearborn (GD) single cationic polymer; Calgon dual-polymer-cationic followed by anionic polymer]. The GD polymer produced a DAF effluent of higher quality (as measured by O/G and turbidity). The optimum dosage for GD polymer was much less variable than that required for the Calgon chemicals. Typically, alteration of the optimum GD dosage was not required for long periods of time, while the opposite was true for the Calgon dual-polymer scheme. However, the amount of sludge produced by the GD polymer was between two and three times greater than for Calgon chemicals, and the combined cost of chemicals and sludge disposal was almost twice as high for the GD chemical. Despite the lower cost associated with using the Calgon dual-polymer system, the use of the GD polymer with DAF was determined to be optimal for this system due to a better quality effluent and a more stable operation. Key words: oily wastewater; metalworking fluids; pilot scale; chemical addition; dissolved air flotation

Wastewater Sludge Dewatering for Champion-Hamilton Treatment Facility

Paper mills are under constant pressure to increase their profits and to reduce their wastewater treatment costs. Champion International Mill in Hamilton, Ohio, is not an exception. The mill produces 340 to 365 tons/day of coated and uncoated printing and writing papers. Prior to 1996, Champion used less than 60 tons/day of secondary fiber. The usage of secondary fiber has increased to 100 to 114 tons/day. In 1996 improvements were made in the mill to reduce fiber losses. At that time the corporation also changed suppliers of polymers. As a result of these changes, the wastewater treatment plant saw its sludge disposal costs increasing. The solids from their screw presses decreased from 55% to 48%. This paper reports the series of options that were examined to improve the dewatering and to lower disposal costs. Included are changes in polymers and polymer applications, changes in the chemical sludge mixing, improved press orifice cleaning, and screw press motor load control systems. The effects of these changes have resulted in improved dewatering and the potential for even higher solids in the sludge cake. The economics of the sludge dewatering system are reviewed.

Phosphorus Recovery Technology Modeling and Feasibility Evaluation for Municipal Wastewater Treatment Plants

A computer model was used to evaluate the economic viability of implementing phosphorus recovery processes in municipal wastewater treatment applications. The model examines investment costs, sludge volumes, sludge disposal costs, chemical costs, and the value of recovered phosphates. The model specifically focused on: 1) representative phosphorus recovery technologies integrated with representative treatment scenarios for enhanced biological nutrient removal (EBNR) with a sidestream Crystalactor® application and for conventional biological treatment followed by mainstream (tertiary) Crystalactor application; 2) the value of recovered phosphorus, assuming recovery as calcium phosphate, with a similar value to that of phosphate ore (handling and transport costs are ignored); and 3) the impacts of phosphorus recovery on major operating costs. The model results show that phosphorus recovery is most cost-effective for high phosphorus and low biochemical oxygen demand (BOD) concentration wastewaters where sludge disposal costs are high. Phosphorus recovery can reduce sludge volumes produced by up to 30 percent (compared to EBNR) and up to 49 percent (compared to chemical phosphorus precipitation). Read-off graphs are also provided for specific conditions to assist facilities in conducting a preliminary assessment of the economics of phosphorus recovery for their facility.

ＡＯＰ処理によるゴミ埋立て地浸出水の凝集性の改善

Coagulation process is usually used as a method of treating refractory substances in wastewater. But, it can't often satisfy target water quality within practical coagulant dosage. In case of treating the effluent from coagulation process, the AOP (Advanced Oxidation Process), an oxidation/decomposition process which combines ultraviolet, ozone, and hydrogen peroxide, is looked upon as a method of treating the effluent from coagulation process. However, the abundant amount of oxidant and ultraviolet irradiation needed for oxidation are hampering the practicalization of this process. The authors conducted a research on the application of the AOP (ozone/hydrogen peroxide treatment) for pretreatment of secondary coagulation process using the effluent from coagulation process of a landfill site leachate treatment plant as raw water. The D-TOC removal by coagulation treatment using AOP treated water of raw water was higher than that using raw water, despite the D-TOC of the former was lower than that of the latter. Considering that the D-TOC removal was occurred during the AOP, it was assumed that the organic compound underwent changes to more susceptible to reaction with coagulant during oxidative decomposition. From this result, it was considered that using the AOP for pretreatment of coagulation process could achieve a significant decrease in coagulant dosage, a space-saving in the sludge treatment facility, and a saving in sludge disposal costs.

Wastewater sludge dewatering for Champion—Hamilton treatment facility

Paper mills are under constant pressure to increase their profits and to reduce their wastewater treatment costs. Champion International Mill in Hamilton, Ohio, is not an exception. The mill produces 340 to 365 tons/day of coated and uncoated printing and writing papers. Prior to 1996, Champion used less than 60 tons/day of secondary fiber. The usage of secondary fiber has increased to 100 to 114 tons/day. In 1996 improvements were made in the mill to reduce fiber losses. At that time the corporation also changed suppliers of polymers. As a result of these changes, the wastewater treatment plant saw its sludge disposal costs increasing. The solids from their screw presses decreased from 55% to 48%. This paper reports the series of options that were examined to improve the dewatering and to lower disposal costs. Included are changes in polymers and polymer applications, changes in the chemical sludge mixing, improved press orifice cleaning, and screw press motor load control systems. The effects of these changes have resulted in improved dewatering and the potential for even higher solids in the sludge cake. The economics of the sludge dewatering system are reviewed.

Optimal Design for Anaerobic Pretreatment of Municipal Wastewater

In recent years the advent of the anaerobic expanded bed reactor (AEBR) has made possible the treatment of wastewaters of comparatively lower strength than have been treated traditionally by anaerobic means. However, regardless of any benefits presented by its use, the process must be shown to be cost effective relative to other options before it will gain acceptance. This paper reports on the results of a series of optimization exercises in which the costs of the AEBR as an expansion alternative for organically overloaded treatment plants are compared with costs for more conventional remedies. The optimization model developed includes the unit processes of primary clarification, AEBR, trickling filtration, secondary clarification, activated sludge, gravity thickening, anaerobic digestion, and vacuum filtration. Several constraint parameters were varied to determine the cases for which the AEBR would be the cost-effective option. These parameters were primary effluent chemical oxygen demand (COD), hydraulic loading, temperature, cost of labor, cost of power, cost of sludge disposal, and amortization interest rate. The results suggest that the AEBR may be a competitive solution for organically overloaded facilities under selected conditions.

Comparison of the cost of the pressurized wastewater treatment process with other established treatment processes

A biological wastewater treatment unit under the influence of pressure was operated at pressures of up to 6 bar. It was demonstrated the capability of operating effectively with high carbonaceous oxidation and nitrification efficiencies at loadings of up to 13 g BOD m −2 day. Another advantage of the pressurized treatment unit was observed to be its low sludge production. The cost of the pressurized treatment unit has, however, become an important factor for the applicability of the pressurized treatment unit. An investigation was carried out to determine the approximate cost of a proposed full-scale pressurized unit. The comparison between the pressurized unit and the established treatment processes were made for three populations of 500, 1000 and 3000 persons. The costs were then compared with those of various other conventional biological treatment processes capable of treating an equivalent wastewater load. The conventional processes selected for comparison were the activated sludge, biological filtration and conventional RBC. The sludge disposal cost for the pressurized unit was appreciably lower than that for the other processes. The results indicated that the cost of the pressurized unit (present value for a 20-yr period) and the costs of the activated sludge and conventional RBC processes were found to be similar for the smaller populations. However, a substantial saving could be obtained with the pressurized unit for the larger populations. In addition, there was an indication that the land requirement of the pressurized treatment unit decreased appreciably as the flow rate increased.

Optimizing phosphorus removal at the Ann Arbor Wastewater Treatment Plant

The Ann Arbor Waste Water Treatment Plant was originally designed as a conventional activated sludge plant. In 1992 it was modified to operate as an A/O plant. Initial operations were difficult and the required phosphorus removal could be obtained only through heavy additions of ferric chloride. Our study focused on the application point of the ferric chloride, and reexamined the major operating parameters of the plant. Paying close attention to parameters such as sludge blanket levels and oxygen concentrations in the aeration tanks lead to an improved phosphorus effluent level of 0.5 mg/l on a continuous basis. Close attention to the oxygen levels in the anaerobic sections also resulted in a better operation. The addition of ferric chloride has been greatly reduced, and thus has lowered the operating costs and the sludge disposal costs.

Optimizing phosphorus removal at the Ann Arbor Wastewater Treatment Plant

The Ann Arbor Waste Water Treatment Plant was originally designed as a conventional activated sludge plant. In 1992 it was modified to operate as an A/O plant. Initial operations were difficult and the required phosphorus removal could be obtained only through heavy additions of ferric chloride. Our study focused on the application point of the ferric chloride, and reexamined the major operating parameters of the plant. Paying close attention to parameters such as sludge blanket levels and oxygen concentrations in the aeration tanks lead to an improved phosphorus effluent level of 0.5 mg/1 on a continuous basis. Close attention to the oxygen levels in the anaerobic sections also resulted in a better operation. The addition of ferric chloride has been greatly reduced, and thus has lowered the operating costs and the sludge disposal costs.

Stabilization and delisting of hazardous wastes: An effective approach for reducing high sludge disposal costs

AbstractDelisting (up‐front or not) of hazardous waste streams (with or without stabilization or any other form of treatment) can be an effective approach for reducing high sludge disposal costs because a nonhazardous classification of the waste will alleviate the financial burden associated with the disposal costs. Facilities may petition EPA to remove individual waste streams from regulation as listed hazardous wastes under the Resource Conservation and Recovery Act (RCRA). EPA encourages the use of up‐front delisting petitions because they have the advantage of allowing the applicant to know what treatment levels for constituents should be sufficient to render specific wastes nonhazardous before investing in new or modified waste treatment systems. Thus, up‐front delisting allows new facilities to receive exclusions prior to generating wastes that, without upfront exclusions, would unnecessarily have been considered hazardous. On July 18, 1991, EPA proposed to use the EPA Composite Model for Landfills (EPACML) when considering delisting petitions and evaluating the impact of the petitioned waste on human health and the environment. The use of the EPACML provides consistency in delisting decisions. Further, this new model allows a two‐to‐three‐times higher dilution than the previously used Vertical and Horizontal Spread (VHS) model. This article presents case studies from several industry sectors where stabilization and delisting were used to manage wastes in a reliable, cost‐effective, and environmentally sound manner.

Solid-bowl centrifuges for wastewater sludge treatment

The recent rapid advances in centrifugal technology for dewatering and thickening of wastewater sludges, against the background of rapidly increasing sludge disposal costs, are described. Examples are given of the key process design factors for wastewater sludge centrifuges, together with performance comparisons with conventional centrifuge technology. As a result of improved digestion, thickening of waste activated sludge can produce savings of 20–30% in the costs of disposal of dewatered digested sludge. Dewatering with advanced centrifuges is shown to have total operating costs for chemicals, personnel, power, capital servicing, transportation and landfill of the sludge at least 30% lower than with conventional technology. The replacement of dewatering equipment should be evaluated if the existing equipment is more than five years old, and the sludge is to be thermally processed or disposed of to landfill.