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Reservoirs for wastewater treatment, storage and reuse.

A must in any wastewater irrigation project

WASTEWATER STORAGE RESERVOIRS ?

In these reservoirs wastewater is stored for long periods of time.
Photo of the 50,000 m3 "Getaot" reservoir.
Photo of one of the wastewater reservoirs of the Metropolitan Tel Aviv.
Photo of the 4.5 million m3 "Hemeq Hepher" reservoir.

The purpose of the storage is twofold:

To release effluents at the desired time of the year (controlled discharge).
To obtain highly quality effluents (wastewater treatment).

Wastewater irrigation projects must match the almost homogeneous sewage flow coming from the city to the discontinuous water demand for irrigation. Wastewater storage reservoirs add flexibility to the operation of the system, optimize the reuse of the reclaimed water, increase the area which can be irrigated, and release effluents of a good and reliable quality.

These wastewater storage and treatment reservoirs can be also applied to other situations:

Coastal areas: Wastewater is stored during the summer in order to avoid the contamination of beaches during the tourism season. By the end of summer -when the last tourist has gone- wastewater will be released from the reservoirs into the sea. Meanwhile, these effluents will reach excellent quality due to long residence time within the reservoirs during the summer months.
River/stream recovery (I): Wastewater is stored during the dry season when the river runs at minimum flow. Wastewater of high quality will be released from the reservoirs to the river when river-flow is at maximum, thus obtaining maximum dilution and minimum negative ecological impact.
River/stream recovery (II): Wastewater is stored when river-flow is at maximum. Wastewater of very high quality is then released from the reservoirs to the river during the dry period as a substitute for freshwater, in order to avoid total drying of the river and ecosystem destruction.
High quality effluents are required. Wastewater contains not only organic matter but also significant concentrations of pathogens, heavy metals, hard detergents, pesticides, organic micro-pollutants and other pollutants which are not removed by the classic sewage treatment plants. Stabilization reservoirs are able to remove most of them.
Cooling water: Wastewater is more and more used as cooling water in power stations and other installations. Wastewater storage reservoirs can supply cooling towers with wastewater of proper quality and temperature in due time.

Besides, stabilization reservoirs are green:

Processes occurring within the reservoirs are natural. They utilize solar energy (mechanical plants use electricity). Algae within the reservoirs produce most of the oxygen required by the processes (mechanical plants take oxygen from the atmosphere, with high energy consumption).
Aquatic birds find the reservoirs a good refuge. This is important in areas where the natural habitat of the birds have been invaded by urban, tourism or agriculture development.

OUR EXPERIENCE WITH STABILIZATION RESERVOIRS.

Stabilization reservoirs have been operated in Israel for more than 30 years for the storage and treatment of wastewater effluents during the wet winter months. The reclaimed water from the reservoirs is then used for agriculture irrigation during the dry summer months.

There are about 200 of these reservoirs in the country. Yet, until recently, criteria for their design and operation as wastewater treatment units were empirical.

We have invested more than 20 years of R &D on the subject, covering the following main topics:

Water balance optimization (input/output, seepage, evaporation, precipitation).
Hydraulics and hydrology.
Limnology
Salts constitution.
Organic loading and oxygen balance.
Removal of BOD, COD, TSS, detergents, heavy metals, nutrients, refractory and other pollutants.
Pathogens (parasites, bacteria, viruses) die-off, inactivation and removal.
Reduction of the clogging capacity of the effluents on the irrigation networks (design tools, operational tools, and the use of 'sanitary' fish to control the biological community).
Nitrification/denitrification.
Computer modelling and simulation.

Today, we have design and operation criteria covering all important parameters (size, shape, maximum depth, inlet/outlet, dead areas, operational regimes, hydraulic loading, surface and volumetric organic loading, and many others). All design and operational criteria are backed by large databases with data from many reservoirs in Israel and other countries. Meanwhile, further R&D continues to be carried out in order to obtain extra information and fine tune the design and operation alternatives (including less important but still significant parameters).

Stabilization reservoirs, as we design them today, are able to remove BOD, COD, detergents and other pollutants by one order of magnitude, while Faecal coliforms are removed by five orders of magnitude (without chlorination).

A BOOK ON WASTEWATER STORAGE RESERVOIRS.

A book which summarizes the experience gained in Israel and abroad on these reservoirs was edited by Dr. Marcelo Juanico from our firm and Prof. Inka Dor from the Hebrew University of Jerusalem.

The complete reference is: M. Juanico and I. Dor (Eds), 1999, “Reservoirs for Wastewater Storage and Reuse”, Springer, Environmental Science Series, Germany, 394 pp. (see the contents)

SOME OF THE TOOLS WE USE FOR THE PROCESS DESIGN OF WASTEWATER STORAGE RESERVOIRS

A mathematical model to analyze and optimize the water balance of the reservoir, including alternative operational regimes, evaporation, seepage, rain, wind, etc.
A mathematical model to analyze and optimize the hydraulic age distribution of effluents within the reservoir working under different operational regimens.
Several statistical models to forecast the removal of BOD, COD, TSS, detergents, and other pollutants.
Two models, one kinetic and one statistical, to forecast pathogens removal.
A statistical model to forecast the oxygen regime of the reservoir, including changes during the year, and day-night cycles at different depths in the water column.
A graphic-mathematical model to simulate wind induced currents at surface and bottom, longshore and rip-currents, in order to select optimal outlet locations.
A kinetic model to simulate and forecast the accumulation and degradation of sludge at the bottom of the reservoir.
A general mathematical meta-model to simulate the interaction between all hydraulic, hydrological, physico-chemical and biological significant processes, forecasting the quality of the effluents as a function of more than 30 design and operational parameters. The effect of 'small' details such as the direction of prevalent winds, the depth of inlet and outlet, and the development or break-down of thermal stratification can be analyzed.
A model for the design and operation of two, three or a whole network of reservoirs working in series and/or parallel.
A model to optimize the integration of advanced stabilization ponds, low-energy aerated lagoons and reservoirs into single high efficient sewage treatment and storage plants.

All these models are not theoretical ones but based on -and verified by- thousands of observations from many different case-studies working under various different operational regimens.

Copyright © 2002-2006 Juanicó - Environmental Consultants Ltd. All rights reserved.
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