fbr rainwater

7/30/2019 Fbr Rainwater

1/22

III.4.1

Rainwater harvesting and reuse

NGO / NPO

Professional Association for

Rainwater Harvesting and Water Recycling

www.fbr.de

Rainwater harvesting and use

Klaus W. Knig

Architect and consulting engineer

Sustainable concepts towards a zero outflow municipality - Zer0-M

Train-the-Trainer Seminar


During the nineties several thousand rainwater harvesting systems have been installed in Germany. The

single components of these installations have been steadily improved, so the rainwater harvesting is acceptedas an progressively, ecological and permanent reliable installation technique. So far the rainwater harvesting

is an important part of the self-sustaining development of rainwater management. The technology of the rain-

water harvesting offers numerous products for different applications scenarios and the installation sizes. In the

mean time a wide range of products are manufactured and are on offer.

This information mentions the most important aspects of rainwater harvesting systems so the future build-

ing owners will not be left alone in respect of the planning and construction of these installations.


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III.4.2


High costs are

diminishing

water consumption

worldwide

Water consumption per capita per year

Water price

Water consumption and price

Rainwater harvesting and use 1

Water consumption and price

Saving of drinking waterIn many regions clean drinking water can only be made available through a huge effort, and therefore it is

always expensive.

Easying the burden of sewers and sewage treatment plantFlooding peaks during heavily rainfall, this hampers the waste water disposal and therefore raises the

costs. These peaks also involve huge damages.

Real future investmentsThe utilization of modern components of installations give a long-term possibility to reduce the consump-

tion of drinking water and the amount of waste water.


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III.4.3


Filtration in front of the tank

Rainwater tanks

Stream in tanks

Important components of rainwater installations


Important components of rainwater installations

Rainwater quality and area of applicationExcellent quality of processed water given by installations with a minimum of technical standards. The qual-

ity of the collected rainwater depends directly on the utilised installation technique. Qualified fixed installations,

which meet the requirements of a minimum standard, supply rainwater (also called process water), which can

be used quite safely for the following mentioned purposes. Processed water from such installations shows,

e.g. in general a better quality than it is required by the Government for bathing and swimming.

Utilization purposes for rainwaterThe process water can be used for toilet-flushing, garden irrigation, for cleaning purposes and for the wash-

ing machine. So the consumption of drinking water can be reduced down to about 50 % of the daily consump-

tion. Due to the soft quality of this rainwater the consumption of washing powder is reduced as well.

Connection of appropriate roof areasOnly roof areas should be connected. So, appropriate roof materials are: schist, clay bricks and concrete

bricks.


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III.4.4


Retention, Utilisation,

Evaporation, Seepage

Substitution of potable water

51 % if the size of the roof and tank

is big enough

Harwested rainwater utilization areas


Harwested rainwater utilization areas

About 50 % of the potable water can be substituted by rainwater in German households. It depends on the

rain, size of the roof, tank size and the number of people in the household.


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III.4.5


Retention, Utilisation,

Evaporation, Seepage

Watering green areas,

flushing toilets, laundry


Applications

Applications

Rainwater can be used in households, commercial and industrial companies, as well as in public organi-

zations, in which it is used for flushing toilets, for cooling purposes, for washing and cleaning systems and forwatering green areas.


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III.4.6


Vortex fine filter for

downpipe installation

Seperating dirt

automatically


Vortex filter

Vortex filter

Filter models and their functions

Filtration in front of the tankA f ilter which is situated in front of the tank is necessary. Until 10 to 15 years ago filters specifically de-

signed for rainwater utilisation were not available. Generally, as in the case of pumps, filters were selected

from those normally used for municipal and for well water. But this type of filters have not been successful for

use in private rainwater utilisation systems.

The selection of the filtration system depends on the constructional situation. Favoured filters show a low

maintenance, a good f iltration capacity and high water harvesting capacity.


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III.4.7


New type cleaning

by Vortex filter


Vortex filter

Vortex filter

There is a multitude of special filters for rainwater harvesting systems that are distinguished by the design,

installation position and functional principle (e.g. filter matting, filter screen). As a general rule filters are to beinstalled in the supply line to the reservoir. They keep unwanted material automatically away from the rainwater

reservoir, that could bring about malfunctions in the system, or make the water quality poorer. Rainfall pipes for

a central location in front of the reservoir are a possible installation places. Furthermore, filters can be directly

located in the rainwater supply line inside of the reservoir.

A distinction is made between filters according to their design with regard to:

Systems with a separate discharge of unwanted material from the filter and

Systems with a retention of unwanted material within the filter.


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III.4.8


ffffdd

Vortex fine filter for

underground

installation

Seperating dirt

automatically


Vortex filter

Vortex filter

Filter in an underground line, ahead of the reservoirIn general the inside diameter of the filter feed line must be uniform throughout, i.e. a tennis ball which en-

ters the filter from the roof must be able to exit through the overflow.

The water loss, or the amount of effluent discharged from filter systems, which are designed so that the

initial flow from roofs can be diverted, should be kept as small as possible.


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III.4.9


Vortex filter

for downpipe and

groundpipe


Vortex filter

Vortex filter

Example for a downpipe and groundpipe filter.


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III.4.10


Filter pit with chamber

for sedimentation

0.6 mm mesh


Filter pit

Filter pit

The rainwater contains finely-distributed solids in small amounts, independent of the filtration of the rain-

water in the supply line of reservoirs. Sedimentation is to be made possible in rainwater reservoirs to removethese solids. Sediment only accrues to a small degree as a rule.

The sedimentation time depends on the density, size and form of the particles and can be precisely de-

termined according to Stokes law. Rainwater reservoirs are reactors with diffuse mixtures, with regard to the

sedimentation as a rule.


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III.4.11


Sinking particle

Heavy metal and bacteria


Sedimentation

Sedimentation

The sedimentation is essentially made possible by the form and arrangement of the supply and overflow

lines, as well as by the water removal, based on empirical knowledge. The sediment in the reservoir does nothave a disadvantageous effect on the water quality, when there is correct maintenance.

The following requirements are to be met in connection with this:

The supply feed should not obstruct the sedimentation with disruptive flows to the extent possibleand existing sediment in the area of the base of the reservoir should not be distributed again. The sup-

plied water is to be distributed broadly and diffusely over the water level, for example, or is to be led in

via a supply pipe to the bottom of the reservoir, and deflected there into an upward flow with a low exist

speed (quiescent supply)

The water removal is to be coordinated in such a way that:

No solids are sucked in (sediment and scum)

Low suction speed is ensured

Flows that are disruptive arise as little as possible

The removal is done in a zone in which the sedimentation has been concluded to a very great degree


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III.4.12



Tank installation

Tank installation with:

Calm inlet

Floating suction filter

1.0 mm mesh

overflow

Tank installation

Inlet feed with stilling chamber for quiescent flow. Even with adequate pre-filtration, some fine sediment

will eventually settle to the bottom of tanks. To prevent this sediment from being disturbed by the flow of in-coming rainwater, the inlet pipe should be brought down to the bottom of the reservoir an then f itted with twin

180 bends, or with an equivalent deflector. This will prevent the water becoming turbid. Another method of pro-

viding uniform and quiescent hydraulic flow is to distribute the inflow into a multiple pipe manifold with many

small outlets holes, which can then be installed on the top of the tank.

From what we know now, reservoirs should only be cleaned after extended time intervals, and never with

chemicals. In the interest of good water quality the tank should not be cleaned too often. Within a short time af-

ter a rainwater systems is installed the bio-film that forms on all wet parts, have a distinct self-cleaning effect.


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III.4.13


Tank installation with:

Calm inlet

Floating suction filter

1.0 mm mesh

Borehole pump

overflow


Tank installation

Tank installation

Floating suctionTurbulence can also be generated if the sediment is disturbed by suction pipe of the process water supply.

The following options are available:

Installing a floating suction system in the reservoir with a plastic float at the end of a flexible pipe

A built-in check valve in the suction line will ensure that the pipe remains filled with liquid, and does not

run empty

Overflow lines are to be attached in such a way that scum in the reservoir is led off

An overflow line is to be provided in the reservoir with the inlet when multiple reservoirs are used


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III.4.14


Comparing water for:

Drinking

Swimming

Rainwater

applications as

Toilet flushing,

Laundry, Watering

green areas


Bacteriological standards and threshold value

Bacteriological standards and threshold value

Collected rainwater which is used in the process water for toilet f lushing, cleaning purposes, garden irriga-

tion and washing, was experimentally contaminated with pathogenic bacteria, Salmonella enteritidis, Yersiniaenterocoliticia and Campylobacter jejuni (Dr. Hollnder, Head of the Department for General hygiene at the

State Testing Laboratory in Bremen, Germany).

The results:

Neither Salmonella enteritidis, Yersinia enterocoliticia nor Campylobacter jejuni are able to grow at tem-

peratures of 5 C, 15 C, 20 C or 37 C

The elimination of Salmonella is supported if the tanks are layered with a biofilm and sediment. So it

could be confirmed, that raised amounts of organic material, pigeon faeces together with optimal tem-

peratures which can be observed accidentally in rain water tanks can not enhance growth of enter-

opathogenic bacteria


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III.4.15


By national law mandatory:

1. Free outlet as protection

against backflow

20 mm air gap


State of the art

State of the art

Supplemental feed systemRainwater harvesting systems have to be provided with a supplemental feed system.

The supplemental feed system has to ensure the operational reliability of the system when there is a drop

below the minimum water volume.

The quality of the water that is fed in on a supplemental basis has to be suitable for the intended purpose.


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III.4.16



2. Labeling the rainwater

distribution pipes


State of the art

State of the art

LabellingProcess water lines are to be clearly and permanently labelled according to the Drinking Water Act. In ad-

dition to this, process water lines are to be labelled with the notice Process Water or Rainwater or Not

Drinking Water.


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III.4.17



3. Labeling the rainwater serving valves

4. The customer must notify the water

supplier prior to the installation


State of the art

State of the art

A sign with a notice is to be installed close to the drinking water inlet of the house or on the water meter of

the building. A graphic symbol according or a sign Not Drinking Water, is to be visibly and permanently at-tached to the removal points. Freely accessible removal points for rainwater are to be secured with a remov-

able or lockable twist lever.


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III.4.18


Rainwater utilisation

for sprinkler and

toilet flushing


Airport terminal B, Frankfurt on Main

Airport terminal B, Frankfurt on Main


19/22

III.4.19


Importing rainwater

from the neighbour


Marburg tennis court

Marburg tennis court


20/22

III.4.20


Importing rainwater

from the neighbour

Joint-Venture

3 winning parties


Automobile washing plant Bommer, berlingen

Automobile washing plant Bommer, berlingen

Rainwater harvesting in industrial and commercial companies started first with car washing.


21/22

III.4.21


Partly supplied office building

Toilet flushing for 14 floors of 25

Economical compact distribution system


Sony-Center, Berlin

Sony-Center, Berlin

Sony Center with rainwater harvestingRain water is used for the toilet flushing and urinals in the Potsdamer Platz office tower, and for irrigation

the recreational outdoor facilities. There is also a reserve supply in case of fire in the office tower. When the

emergency storage is full, surplus water is diverted into the combined sewer system at a rate of 14 34 m/h.

When no rainwater is available the system can be supplemented with municipal water.


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