Sludge Treatment Facilities Research Articles

Operation of Centralized Sludge Treatment Facilities

Construction of sewerage systems in the city of Yokohama has proceeded at a rapid pace ever since the first wastewater treatment plant went into operation in 1962. By 1984, all eleven of the planned wastewater treatment plants were in operation. By March 1989, the sewerage service rate had reached 80 percent, representing over 2.56 million of the city's residents. Naturally, the expansion of the sewerage system was reflected in a commensurate increase in the quantity of sludge for treatment and disposal. Recognizing the critical importance of keeping abreast of this increase, the city has promoted the development of technology for more efficient treatment and disposal of sludge throughout the intervening years. In recent years, the city has also seen extensive urbanization and mounting concern among its citizenry for conserving the environment. In response, it was decided to shift from the former decentralized method of sludge treatment (i.e., treatment of sludge at the plant generating it) to a method of centralized treatment at two sludge treatment centers, each built within a different wastewater treatment plant located in the waterfront area. Yokohama was the first city in Japan to adopt this form of centralized sludge treatment. The construction of the centralized sludge treatment facilities made extensive use of results from a program of technological development. The centers feature the first egg-shaped digestion tanks, a high-concentration mode of digestion made possible by the use of centrifugal thickeners, power generator fueled with digestion gas, effective use of the waste heat from these generators, and the saving of fuel by the use of incinerators equipped with dryers. The record for the first year of full-scale operation clearly demonstrated the merits of centralized treatment. The quantity of digestion gas generated at the center was double that of the quantity generated under the former method for an equivalent quantity of sludge. Power generation fueled by digestion gas supplied 64 percent of the center's own power needs. While operating at only one-fifth of the planned sludge capacity, the center boasted a savings of about 200 million yen for the year, and the treatment costs were less than half of the treatment cost of the same quantity utilizing the former method. This report presents an account of the operational record for the first year of this center (the Hokubu Sludge Treatment Center) and the system of effective energy use that took place in it.

Oxidation of hydrogen sulfide by flocculated Thiobaccillus denitrificans in a continuous culture

In a continuous fermentation, significant advantages may be gained by immobilization of microbial cells. Immobilization allows cells to be retained in the fermenter or to be readily recovered and recycled. Therefore, the hydraulic retention time and the biomass retention time are decoupled. A novel cell immobilization has been developed for the immobilization of autotrophic bacteria by coculture with floc-forming heterotrophic bacteria with growth of the latter limited by the availability of organic carbon. The result is an immobilization matrix which grows along with the immobilized autotroph. We have previously demonstrated the utility of this approach by immobilizing the chemoautotroph Thiobacillus denitrificans in macroscopic floc by coculture with floc-forming heterotrophs from an activated sludge treatment facility. Floc with excellent settling characteristics were produced. These floc have now been used to remove H(2)S from a gas stream bubbled through continuous cultures. The stoichiometry and kinetics of H(2)S oxidation by immobilized T. denitrificans were comparable to that reported previously for free-cell cultures. Oxygen uptake measurements indicated the growth of both T. denitrificans and the heterotrophs although the medium contained no added organic carbon. Continuous cultures with total biomass recycle were maintained for up to four months indicating the long-term stability of the commensal relationship between the immobilized autotroph and the heterotrophs which composed the immobilization matrix. It was observed that at any given H(2)S loading the biomass concentration reached a maximum and leveled out. The ultimate biomass concentration was dependent upon the H(2)S feed rate.

Novel immobilized cell reactor for microbial oxidation of H 2S

In a continuous fermentation, significant advantages may be gained by immobilization of microbial cells. Immobilization allows cells to be retained in the fermenter or to be readily recovered and recycled. A novel cell immobilization has been developed for the immobilization of autotrophic bacteria by coculture with floc-forming heterotrophic bacteria with growth of the latter limited by the availability of organic carbon. The result is an immobilization matrix which grows along with the immobilized autotroph. The chemoautotroph Thiobacillus denitrificans has been immobilized in macroscopic floc by coculture with floc-forming heterotrophs from an activated sludge treatment facility. Floc produced were subsequently used to remove H 2S from a gas stream bubbled through a continuous culture with total biomass recycle. The ultimate biomass concentration was dependent upon the H 2S feed rate and the H 2S removal efficiency was influenced by the biomass concentration.

Design of Anaerobic Digestion of Lime Sludges

Previous work has demonstrated that inhibition of volatile solids destruction during anaerobic digestion occurs at elevated calcium levels. In this work, calcium inhibition has been taken into account in the design of a treatment facility digesting sludges which contain lime from phosphorous removal. A conventional activated sludge treatment facility has been designed along with a facility removing phosphorous by lime addition to primary clarifiers. Unit sizing, costs and energy requirements are compared and discussed.

A comparison of two-stage and six-stage Andersen impactors for viable aerosols

The widely used Andersen six-stage air sampler for viable aerosols was compared with the more recently available metallic (non-disposable) two-stage sampler at several wastewater and wastewater sludge treatment facilities. Both bacterial indicator organisms and fungi were measured using biological media appropriate for each. The two sampling instruments were mounted on a single tripod and simultaneous side-by-side air samples were collected. These samples were processed in an identical manner and the data was analyzed to yield bacterial and fungal colony forming units per cubic meter of air for each of the sampling devices. In order to determine a baseline of variability between sampling devices in the field, samples were also collected using two six-stage samplers side-by-side and two two-stage samplers side-by-side. This research was undertaken to determine by statistical analysis whether results using the non-disposable two-stage sampler are different from those using the six-stage sampler under field ...

Effects of Scheduling Municipal Waste‐Water Effluent Irrigation of Reed Canarygrass on Nitrogen Renovation and Grass Production

AbstractA 2‐year field experiment was conducted to test the performance of reed canarygrass (Phalaris arundinacea L.) and the removal of nitrogen from municipal waste‐water effluent under varying irrigation schedules. The effluent was obtained from an activated sludge treatment facility that served a domestic suburban population. The 1st‐year total application to the 12‐ by 12‐m plots was about 170 cm of effluent containing 320 kg/ha N, primarily in the ammonia form. The 2nd‐year application consisted of about 290 cm of effluent containing $30 kg/ha N. Treatments during both years were comprised of 1, 2, or 5 irrigations per week. Results indicated that there was no effect of varying the irrigation schedule on the reed canarygrass yields, which averaged 10.2 and 15.0 metric tons/ha during the 1st and 2nd year, respectively. There also was no effect on soil water N concentrations, which averaged 1.0 and 2.4 mg/liter during the 1st and 2nd year, respectively.

Attitudes in Sludge Treatment and Disposal

In addition to improving the technology, there is a need to reassess some of the attitudes which have influenced present sludge management schemes. While the focus for many sludge management systems is sludge dewatering, removal of water from sludge may not be necessary or economically feasible in all instances. It is suggested that not all wastewater treatment facilities should have sludge treatment and disposal facilities—indeed, regional sludge management facilities may be preferable even for the largest cities. Present waste management practices often result in admitting waste constituents to sewerage systems which seriously interfere with all conceivable sludge management practices. Additionally, some present sludge management practices do not adequately recycle or dispose of sludge, but merely stockpile it for future generations.

The temperature dependency of biological denitrification

Biological denitrification of wastewater using denitrifying forms of bacteria found in activated sludge is one of the currently proposed methods for nitrogen removal. The reduced biological activity associated with decreases in temperature is a particularly important parameter of biological denitrification where wastewater temperatures may decrease to approximately 5°C during the winter. Laboratory batch denitrification tests on a defined media utilizing a dominant culture of Pseudomonas denitrificans illustrate that the temperature dependency of the specific denitrification rate can be closely approximated by an Arrhenius temperature relationship. Linear nitrate and carbon removal rates were obtained following an initial lag period which increased with decreasing temperature. Rates ranging from 0.013 at 5°C to 0.16 mg NO a as N mg −1 of organisms h −1 at 27°C were observed. Data from tests using admixtures of activated sludge indicated that a significant number of denitrifying microorganisms were naturally present. Overall denitrification rates corresponding to those of Pseudomonas denitrificans would be observed when the suspended solids were 2.5–4.0 times those of the pure culture. From these studies it would appear that successful biological denitrification units can be designed in conjunction with existing activated sludge treatment facilities producing a nitrified effluent under winter conditions.