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PubMed2005

Modeling the influence of temperature on degree of concentration polarization in reverse osmosis systems.

A model describing the influence of temperature on degree of concentration polarization is proposed. The model is based on the following assumptions: (1) membrane morphology is temperature-independent; (2) transport characteristics of membrane are invariant with coordinate; (3) specific water permeability of the membrane is based on exponential dependence of viscosity vs. temperature; (4) temperature-dependence of membrane rejection is assumed to be linear. Proposed models permit quantitative correlations of longitudinal mass flow and degree of concentration polarization at different operating temperatures. It enables analysis of the influence of temperature, mass flow, bulk concentration, axial velocity, channel geometry, physical properties and membrane rejection on longitudinal distribution of concentration polarization degree. The submitted model does not contain digital integration and can be segmented into optimization algorithms.

Algorithms↗
PubMed2005

Waste stabilisation ponds in France: state of the art and recent trends.

Waste stabilisation ponds represent 20% of the total number of wastewater treatment plants in France. Practical expertise acquired during these last 20 years has led to modification in the design of the first facultative basin of WSP systems. Its active surface area is now dimensioned at 6 m2(p.e.)(-1) in order to limit the risk of malfunctioning. The cumulated surface of the 2nd and 3rd basin is maintained at 5 m2(p.e.)(-1). Another practical point is also that WSPs must receive mainly diluted influents. Globally, the plants are on average far from their nominal loadings, which explains why the first sludge removals took place on average 13 years after being put in operation. Based on a representative sample of plants, i.e. 1 5% of the French WSPs, it has been possible to estimate the time, material means and cost needed for sludge removal as well as the amount of sludge accumulated. The sludge removed at the 1st yields on average 110 L (p.e.)(-1) which represents 12 kg DM (p.e.)(-1). The current trend of increasing the quality levels necessary for discharge into sensitive receiving bodies has led to adaptive solutions of polishing treatments by intermittent sand filter systems with or without the plantation of reeds.

Facility Design and Construction↗
PubMed2005

Changes in waste stabilisation pond performance resulting from the retrofit of activated sludge treatment upstream: part II--Management and operating issues.

Bolivar Wastewater Treatment Plant (WWTP) was originally commissioned with trickling filter secondary treatment, followed by waste stabilisation pond (WSP) treatment and marine discharge. In 1999, a dissolved air flotation/filtration (DAFF) plant was commissioned to treat a portion of the WSP effluent for horticultural reuse. In 2001, the trickling filters were replaced with activated sludge treatment. A shift in WSP ecology became evident soon after this time, characterised by a statistically significant reduction in algal counts in the pond effluent, and increased variability in algal counts and occasional population crashes in the ponds. While the photosynthetic capacity of the WSPs has been reduced, the concomitant reduction in organic loading has meant that the WSPs have not become overloaded. As a result of the improvement in water quality leaving the ponds, significant cost savings and improved product water quality have been realised in the subsequent DAFF treatment stage. A number of operating issues have arisen from the change, however, including the re-emergence of a midge fly nuisance at the site. Control of midge flies using chemical spraying has negated the cost savings realised in the DAFF treatment stage. While biomanipulation of the WSP may provide a less aggressive method of midge control, this case demonstrates the difficulty of predicting in advance all ramifications of a retrospective process change.

Agriculture↗
PubMed2005

Wastewater stabilisation ponds: Sludge accumulation, technical and financial study on desludging and sludge disposal case studies in France.

Waste stabilisation pond treatment was widely developed during the 1980s in France, where there are now over 3,000 plants. Desludging the ponds has now become essential. In 19 primary facultative ponds, in operation for 12-24 years, the net average sludge accumulation rate was 19 mm/yr. The average per capita accumulation rates ranged from 0.04-0.148 m3/person.year (mean of 0.08 m3/person.year). In primary facultative ponds the volume of sludge represented 15-39% of the total volume of the basin. A filling rate above 30% necessitates desludging. In France, a desludging interval of 15 years is recommended for primary facultative ponds. The cost evaluation of desludging and landspreading showed differences according to the desludging technique used. Desludging after emptying the water had an average cost of 38 Euro/m3 of sludge with 10% dry solid (range from 20 to 83 Euro/m3). Under-water desludging was 50% more expensive. Although desludging is carried out only after several years of operation, its cost must be allowed for in the annual operation and maintenance costs of the process. It can be estimated to be 3 ł/person.year. Even with this additional cost, waste stabilisation pond treatment remains less expensive than other treatment processes.

France↗
PubMed2005

Sustainable management of leakage from wastewater pipelines.

Wastewater pipeline leakage is an emerging concern in Europe, especially with regards to the potential effect of leaking effluent on groundwater contamination and the effects infiltration has on the management of sewer reticulation systems. This paper describes efforts by Australia, in association with several European partners, towards the development of decision support tools to prioritize proactive rehabilitation of wastewater pipe networks to account for leakage. In the fundamental models for the decision support system, leakage is viewed as a function of pipeline system deterioration. The models rely on soil type identification across the service area to determine the aggressiveness of the pipe environment and for division of the area into zones based on pipe properties and operational conditions. By understanding the interaction between pipe materials, operating conditions, and the pipe environment in the mechanisms leading to pipe deterioration, the models allow the prediction of leakage rates in different zones across a network. The decision support system utilizes these models to predict the condition of pipes in individual zones, and to optimize the utilization of rehabilitation resources by targeting the areas with the highest leakage rates.

Decision Making↗
PubMed2005

Natural recharge to sustainable yield from the barind aquifer: a tool in preparing effective management plan of groundwater resources.

This paper presents the results of water balance study and aquifer simulation modeling for preliminary estimation of the recharge rate and sustainable yield for the semi arid Barind Tract region of Bangladesh. The outcomes of the study are likely to be useful for planning purposes. It is found from detailed water balance study for the area that natural recharge rates in the Barind Tract vary widely year to year. It may have resulted from the method used for the calculation. If the considered time interval had been smaller than the monthly rainfall, the results could have been different. Aquifer Simulation Modeling (ASM) for the Barind aquifer is used to estimate long-term sustainable yield of the groundwater considering limiting drawdown from the standpoint of economic pumping cost. In managing a groundwater basin efficiently and effectively, evaluation of the maximum annual groundwater yield of the basin that can be withdrawn and used without producing any undesirable effect is one of the most important issues. In investigating such recharge rate, introduction of certain terms such as sustainable yield and safe yield has been accompanied. Development of this area involves proper utilization of this vast land, which is possible only through ensured irrigation for agriculture. The Government of Bangladesh has a plan to develop irrigation facilities by optimum utilization of available ground and surface water. It is believed that the groundwater table is lowering rapidly and the whole region is in an acute state of deforestation. Indiscriminate groundwater development may accelerate deforestation trend. In this context estimation of actual natural recharge rate to the aquifer and determination of sustainable yield will assist in proper management and planning of environmentally viable abstraction schemes. It is revealed from the study that the sustainable yield of ground water (204 mm/y) is somewhat higher than the long-term annual average recharge (152.7 mm) to the groundwater reservoir. The reason behind this is that the rivers within and around the Barind Tract might have played the role of influent rivers.

Agriculture↗
PubMed2006

[Characteristics of aerobic granular sludge membrane bioreactor for wastewater treatment].

Characteristics of aerobic granular sludge membrane bioreactor (MBR) and the membrane fouling were studied with synthetic wastewater. Experimental results showed that COD removal rate could be reached over 96% under the conditions of HRT = 6h, DO 4 - 6 mg x L(-1) and the volumetric load of COD = 7.24 kg x (m3 x d)(-1). When the volumetric load of NH3-N was 0.17 kg x (m3 x d)(-1), the removal rate of NH3-N was about 60%. The variations of the COD/N ratio could not affect the removal of COD and NH3-N. During the stable operation process, MLSS of the reactor was as high as 14 - 16 mg x L(-1), which could conduce simultaneous nitrification-denitrification, as the anoxic and anaerobic microorganisms might be existed in the core of granular sludge. In addition, the membrane flux of MBR of two different configurations of sludge, granular sludge and floccular sludge, was compared. The flux reduction of granular sludge MBR was much lower than that of floccular sludge MBR. Moreover, the membrane permeability of the granular sludge MBR could be regained simply by backwashing with aeration or washing the membrane with water.

Bacteria, Aerobic↗
PubMedDate not supplied

Wastewater reuse for agriculture: regional health perspective.

The Eastern Mediterranean Region of the WHO is the poorest region in the world in water resources as a Region and per capita. This paper summarizes existing practices and constraints regarding wastewater treatment and reuse in the Region and describes the health impact of inappropriate practices. Appropriate treatment for agricultural use from the health point of view, and the health regulations and guidelines for wastewater reuse in the Region are outlined. The work of the WHO Regional Office to assist countries face the challenges of water scarcity and wastewater reuse are described. Finally, key suggestions that could enhance the use of reclaimed wastewater while at the same time safeguarding human health are presented.

Agriculture↗
PubMedDate not supplied

[Liquid hospital waste].

Hospital sewage is distinct both from that of industrial origin and that from human housing, and is unique from the qualitative and quantitative standpoints. In fact the hospital is clearly different from a residential setting for the addition of technological activities, which are realised inside it, and it is not comparable to a traditional productive complex, because of the extreme variability--from one hospital to the other--of the presence of activities themselves, and this means important quali--quantitative differences of sewage produced from case to case. After all, the hospital cannot be compared to a centre of tertiary activities, which has, as regards sewage, the characteristics and the constancy of great inhabited places. Actually, its daily amount per patient is up to 1,000 L (3-5 times more than a standard citizen), because hospitals include, besides patients, physicians, nurses, technical and clerical staff and, for "teaching hospitals", also professors and students; in addition, the sewage from hospitals is composed of standard human sewage, plus: discharges from laboratories and technical equipments; drugs and their metabolites; disinfectants; and microorganisms, which are often characterized by the presence of antibiotic resistance of "infectious" nature (i.e. transmitted by resistance plasmids). Such contaminants are not evenly generated, but focal points in the hospital and given hours during the day can help to identify where and when most of each contaminant is produced. A special problem arises from the interference of contaminants in hospital sewage on activated sludge plants; another is connected with the presence of toxic substances originated from biochemical laboratories, but the concentration of such substances appears to be lower than that tolerated according to the italian regulations.

Containment of Biohazards↗
PubMed1989

Managing hazardous waste in the clinical laboratory.

Clinical laboratories generate wastes that present chemical and biologic hazards. Ignitable, corrosive, reactive, toxic, and infectious potentials must be contained and minimized. A summary of these problems and an overview of the applicable regulations are presented. A checklist of activities to facilitate the annual review of the hazardous waste program is provided.

Hazardous Waste↗
PubMed1989

[Ionogenic liberation of mercury from dental amalgam in waste water and sludge].

Reduction of mercury content in communal waste water and sludge is mandatory. The release rate of Hg from dental amalgam (gamma 2 Lux Alloy) in waste water was determined. The Hg-ionic rate was found to be as low as 0.004% of total mercury content in waste water. In addition, the concentration of Hg (4.39-8.20 mg/kg), Ag (73.35-84.03 mg/kg and Sn (22.51-61.30 mg/kg) in sludge was estimated under anaerobic conditions. Compared with legal limits for drinking water (1 microgram Hg/l) in the F.R.G. mercury loads of dental surgeries are far below threshold levels where toxicological effects are to be expected.

Dental Amalgam↗