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WE
HAVE THE TECHNOLOGY
Waste Water Treatment Plants
Architect
Ami Ran & Dr. Yair Folkman
"Heredity is a strong factor, even in architecture.
Necessity first mothered invention. Now invention has little ones
of her own, and they look just like grandma."
E. B. White.
Most architects are fascinated by "mechanized buildings"
- power stations, windmills and wells. Given these current dry times,
a review of water purification facilities - some of which demonstrate
simple, good architecture - may be timely.
In principle, the law charges anyone who creates sewage to purify
and dispose of it appropriately, without causing sanitary or environmental
hazards. We simple citizens are not equipped to purify our own sewage,
so the Local Municipality Law of 1962 places the burden on local authorities.
who must ensure that sewage disposal is conducted without polluting
water and land resources nor serve or attracting mosquitoes, flies
and other pests. To make the job palatable, local authorities are
legally entitled to levy fees and taxes on its citizens and businesses,
to fund construction of sewerage systems and treatment plants.
Those thirsty for facts and figures may be interested in learning
that in Israel, total annual private and industrial water consumption
reaches 500 million cubic meters. Of these 325 undergoes purification,
but only 125 million cubic meters are processed for reuse. The rest
is discharged into the Mediterranean. The agricultural sector in Israel
is the greatest consumer of water (1,252 million cubic meters, at
subsidized rates). If the 200 million cubic meters of purified water
were utilized for irrigation purposes, the future of the Sea of Galilee,
currently on the verge of ecological collapse due to over-pumping,
could be ensured.
The Water Commissioner has at his disposal some $200
million for the waste water utilization. Its use, however, is conditionable
on the building of sufficient reservoirs to store winter rainfall.
Until then, discharge of purified water directly into the sea will
continue.
Waste water treatment plants must meet two parallel challenges: the
prevention of environmental pollution and the enrichment of national
resources. This is not only essential but also feasible. The valuable
byproducts of sewage purification can be fully utilized - organic
fertilizer for enrichment of soil, clear gray water for irrigation,
and methane gas as a source of energy.
How it works
The treatment plants separates the solids, less than half a percent
of sewage, and purifies the liquids through a process of primary and
secondary filtering, primary sludge settling, sorting, aeration, secondary
sludge settling and treatment and drying of the sludge for disposal.
Facilities are generally based on controlled physical-biological processes.
Treatment begins with the simple separation and settling, graduating
to processes based on higher cost-efficiency ratios.Mechanical filters
constructed of horizontal poles separate rags, paper, plastic and
other substances, which are then compressed and transferred to containers.
The sewage is transferred to sand traps where the heavier substances
such as sand and seeds settle before being rinsed and collected into
containers.
Activated sludge process
This calls for a primary sludge settling process in oval concrete
pools; rakes at the bottom collect the organic substances. The next
stage is an an-aerobic process in the aeration secondary settling
pools. Colonies of bacteria develop, nourished by the organic substances
and oxygen integrated into the sewage through a constant stirring
process. In the settling pool, the colonies settle to the bottom as
active sludge, while the clear gray water lies at the surface. The
active sludge is collected and most of it is returned to the aeration
pool, in order to thicken the concentration of germs and make the
process more efficient. The remaining sludge is transferred to the
treatment pool.
Continuous oxidation
This method is based on an activated sludge process combined with
extended aeration. It omits the primary settling stage and facilitates
full oxidation of organic substances which renders small quantities
of sludge, calling for a less complicated treatment prior to disposal.
While this processes calls for higher energy consumption, the omission
of the primary settling stage and the reduced quantities of sludge
simplifies the process and reduces the treatment plant's running costs.
The continuous oxidation pools have canals connected in a line with
aerators which supply oxygen and drive the mixed liquids along the
canals. Oxygen is added a second time, and in each canal different
nitrogen deterring processes occur.
Water treatment
The sludge produced is 75% organic matter which can be used, with
simple additional treatment, as a source of energy or as organic fertilizer
. In treatment plants utilizing the activated sludge method, sludge
is stabilized through a process of organic digestion. The primary
and remaining sludge is transferred to the digester pools for transformation
into methane gas, carbon dioxide and water over a period 15-20 days.
To facilitate the disposal of sludge in trucks or containers, it must
be dried and transformed into solid waste on condition it is free
of toxic matter and heavy metals which are common components of industrial
waste.
Given that appropriate technological treatment allows for retention
of some 98 per cent of sewage water available for recycling to agriculture,
industry, or irrigation of public parks, the country's high quality
drinking water should be exclusively for domestic consumption. We
have the technology to turn the country's waste water into purified,
odorless and recyclable water for our fields, orchards, parks, and
lawns. Or, we can continue to throw it all away into the Mediterranean
Sea.
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