Economic feasibility study for wastewater treatment: A cost-benefit analysis

Water resource management should be made from a multidisciplinary perspective. In this sense, economic research into the design and implementation of policies for the efficient management of water resources has been emphasized by the European Water Framework Directive (WFD). Cost-benefit analysis (CBA) is one of the more widely accepted economic instruments since it is a rational and systematic decision-making support tool. Moreover, the wastewater treatment process has significant associated environmental benefits. However, these benefits are often left uncalculated because they have no market value. In this paper, using the concept of shadow price, a quantification of the environmental benefits derived from wastewater treatment is made. Once the environmental benefits are estimated and the economic costs of the treatment processes are known, a CBA is made for each of the wastewater treatment plants (WWTPs) under study. In this way, a useful economic feasibility indicator is obtained for WWTP operation.     

Economic and environmental benefits of thermal insulation of building external walls

Thermal modernization is viewed by its users in Poland mainly in terms of economic benefits. Nevertheless, it does not reduce the significant role of thermal modernization in lowering the environmental impact at the phase of a building use. The paper presents economic and environmental benefits due to thermal insulation of building external walls.     

Economic evaluation of alternative wastewater treatment plant options for pulp and paper industry

Excessive water consumption in pulp and paper industry results in high amount of wastewater. Pollutant characteristics of the wastewater vary depending on the processes used in production and the quality of paper produced. However, in general, high organic material and suspended solid contents are considered as major pollutants of pulp and paper industry effluents. The major pollutant characteristics of pulp and paper industry effluents in Turkey were surveyed and means of major pollutant concentrations, which were grouped in three different pollution grades (low, moderate and high strength effluents), and flow rates within 3000 to 10,000 m³/day range with 1000 m³/day steps were used as design parameters. Ninety-six treatment plants were designed using twelve flow schemes which were combinations of physical treatment, chemical treatment, aerobic and anaerobic biological processes. Detailed comparative cost analysis which includes investment, operation, maintenance and rehabilitation costs was prepared to determine optimum treatment processes for each pollution grade. The most economic and technically optimal treatment processes were found as extended aeration activated sludge process for low strength effluents, extended aeration activated sludge process or UASB followed by an aeration basin for medium strength effluents, and UASB followed by an aeration basin or UASB followed by the conventional activated sludge process for high strength effluents.     

Seasonal tertiary wastewater treatment in California: an analysis of public health benefits and costs

A number of communities in the Central Valley of California have requested that seasonally based effluent limits be developed for their wastewater treatment facilities. These seasonal limits would be based on disinfected secondary treatment during the winter and disinfected tertiary treatment during the rest of the year. Such a request for seasonal limits raises a significant water quality policy question with regard to the costs and relative benefits of tertiary treatment during the winter season. A benefit-cost analysis for winter season tertiary wastewater treatment in California's Central Valley is presented here. The assumed societal benefit of winter tertiary treatment is enhanced water quality for recreational purposes, and thus reduced risk to public health. Based on the results of this analysis, between four and sixteen million recreation events would need to occur annually region-wide during the winter to justify the costs of winter tertiary treatment. A similar method and the information described herein could be used by the state water quality regulatory agency to develop a risk-based policy to consider seasonal limits.     

An integrated environmental plan for the reuse of treated wastewater effluents from WWTP in urban areas

The reuse of treated wastewater effluents from wastewater treatment plants (WWTP) is a recent practice in the environmental restoration of marginal areas in combination with tree and shrub planting. In urban areas, an integrated approach to the application of this practice implies (a) reuse of treated domestic wastewater for irrigation of hardy plant species and (b) design of environmentally friendly outdoor landscape including the planting of species acceptable for irrigation with such kind of wastewater.     

Microalgae growth-promoting bacteria as "helpers" for microalgae: a novel approach for removing ammonium and phosphorus from municipal wastewater

A combination of microalgae (Chlorella vulgaris or C. sorokiniana) and a microalgae growth-promoting bacterium (MGPB, Azospirillum brasilense strain Cd), co-immobilized in small alginate beads, was developed to remove nutrients (P and N) from municipal wastewater. This paper describes the most recent technical details necessary for successful co-immobilization of the two microorganisms, and the usefulness of the approach in cleaning the municipal wastewater of the city of La Paz, Mexico. A. brasilense Cd significantly enhanced the growth of both Chlorella species when the co-immobilized microorganisms were grown in wastewater. A. brasilense is incapable of significant removal of nutrients from the wastewater, whereas both microalgae can. Co-immobilization of the two microorganisms was superior to removal by the microalgae alone, reaching removal of up to 100% ammonium, 15% nitrate, and 36% phosphorus within 6 days (varied with the source of the wastewater), compared to 75% ammonium, 6% nitrate, and 19% phosphorus by the microalgae alone. This study shows the potential of co-immobilization of microorganisms in small beads to serve as a treatment for wastewater in tropical areas.     

Determining the mechanisms for aerobic granulation from mixed seed of floccular and crushed granules in activated sludge wastewater treatment

Aerobic granulation is a novel and promising technology for wastewater treatment. However, long start-up periods required for the development of granules from floccular sludge, and the loss of biomass in this period leading to poor nutrient removal performance are key challenges. In a recent study the addition of crushed granules to a floccular sludge significantly reduced the start-up period, and also maintained the nutrient removal performance during granulation. In this study, we examined the mechanisms responsible for the fast granulation from a mixture of floccular and granular sludges. Fluorescent microbead particles (4 μm diameter) were successfully applied to differentially label the surfaces of floccular and crushed granular aggregates. Labelled flocs and crushed granules were added to a laboratory scale wastewater treatment reactor, and the granule formation process was monitored using confocal laser scanning microscopy over an 80 day period. Flocs were observed to attach to the surface of the seeding granules, resulting in reduced biomass washout during granulation. This mechanism not only reduces the granulation period, but also maintains the nutrient removal performance of the reactor. The results indicate that the granules acted as nuclei for floccular particle attachment, which accelerated granule formation.     

Nitrous oxide emissions from secondary activated sludge in nitrifying conditions of urban wastewater treatment plants: effect of oxygenation level

In order to better understand the mechanisms of N(2)O emissions from nitrifying activated sludge of urban WWTPs, sludge from the Valenton plant (Paris conurbation) are subjected to lab-scale batch experiments under various conditions of oxygenation. The results show that the highest N(2)O emissions (7.1 microgN-N(2)OgSS(-1) h(-1) in average) occur at a dissolved oxygen (DO) concentration of around 1mgO(2)L(-1). These high emissions at low oxygenation (from 0.1 to 2 mg O(2)L(-1)) are due to two processes: autotrophic nitrifier denitrification and heterotrophic denitrification. Nitrifier denitrification always dominates, representing from 58% to 83% of the N(2)O production. This N(2)O production originating from nitrifying activated sludge becomes 8 times higher when nitrite is added at a DO of 1 mg O(2)L(-1); a decrease is observed both at higher and lower oxygenation. Heterotrophic denitrification represents less than 50% of the N(2)O production, decreasing from 42% to 17% when oxygenation increases from 0.1 to 2 mg O(2) L(-1). We show that ammonium oxidizing bacteria (AOB) can shift to nitrifier denitrification when oxygen is depleted in the environments including in the WWTPs, nitrite then plays the role of oxygen as the final electron acceptor. As opposed to what happens in nitrification, the end products of nitrifier denitrification are gaseous forms of nitrogen, where N(2)O is not negligible compared to N(2). Overall, N(2)O emissions represent 0.1-0.4% of oxidized NH(4)(+), depending on the oxygenation level. N(2)O emissions would range from 0.11 to 0.42 TN-N(2)O day(-1) for a tertiary treatment of the Paris wastewater effluents, consisting exclusively of activated sludge nitrification.     

Hyperconcentrated cultures of Scenedesmus obliquus: A new approach for wastewater biological tertiary treatment?

Algal cultures of Scenedesmus obliquus at low concentrations (0.1–0.2 g dry wt l⁻¹) provide adequate biological tertiary treatment of wastewaters. This research was aimed at studying the possibility of increasing the system performance by using hyperconcentrated cultures of S. obliquus (up to 2.6 g dry wt l⁻¹) at the laboratory scale. The algal culture grown on secondary effluent was first chemically flocculated with chitosan (30 mg l⁻¹) and decanted; the sedimented culture (5 g dry wt l⁻¹) was then resuspended in secondary effluent to obtain algal suspensions at various concentrations, the performance of which was compared to that of a control culture (0.13 g dry wt l⁻¹). The rate of exhaustion of nitrogen (N-NH₄⁺) was proportional to the algal concentration and a complete removal could be obtained within 15 min (at 2.6 g dry wt algae l⁻¹); this result compares favorably to the 2.5 h or so required by the control culture. The unit uptake rate for nitrogen (N-NH₄⁺) had a tendency to increase with the algal concentration, whereas that of phosphorus (P-PO₄³⁻) showed the opposite relationship. Considering the results obtained, it appears that hyperconcentrated algal cultures have a high potential for the tertiary treatment of wastewaters; a significant reduction of pond surface for large scale operations can be anticipated.     

Algal wastewater treatment systems for seasonal climates: application of a simple modelling approach to generate local and regional design guidelines

Algal waste stabilisation ponds (WSP) provide a means of treating wastewater, and also a potential source of water for re-use in irrigation, aquaculture or algal biomass cultivation. The quantities of treated water available and the periods in which it is suitable for use or discharge are closely linked to climatic factors. This paper describes the application, at a continent-wide scale, of a modelling approach based on the use of readily available climate datasets to provide WSP design and performance guidelines linked to geographical location. Output is presented in regionally-based contour maps covering a wide area of Russia and central Asia and indicating pond area, earliest discharge date, discharge duration, wastewater inflow:outflow ratio and salinity under user-specified conditions. The results confirm that broad-brush discharge guidelines of the type commonly used in North America can safely be applied; but suggest that a more detailed approach is worthwhile to optimise operating regimes for local conditions. The use of long-series climate data can also permit tailoring of designs to specific sites. The work considers a simple 2-pond system, but other configurations and operating regimes should be investigated, especially for the wide range of locations across the world that are intermediate between the ‘one short discharge per year’ mode and year-round steady-state operation.     

An introduction of a multi‐soil‐layering system: a novel green technology for wastewater treatment in rural areas

Multi‐soil‐layering (MSL) systems are designed for municipal wastewater, livestock wastewater and polluted river water treatments. They are mainly composed of soil mixture block layers and water‐permeable layers (PL). The MSL system overcomes many of the shortcomings of conventional soil treatment systems such as easy clogging, large land requirement and low hydraulic loading rate. This paper summarizes the structure, purification mechanism and practical application of the systems for different kinds of wastewater treatment. The paper also compares MSL systems with other decentralized systems such as wetland and compact filter systems in their respective structures and treatment efficiencies. Finally, the paper gives a rough evaluation of the lifespan and cost of an MSL system based on its material composition.