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Watercourse protection facilities
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- Description
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- Key elements
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- Stationary equipment
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- Mobile equipment
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Description
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A watercourse protection facility suits the purpose of purification of waste water
from tunnelling in order to preserve criteria for discharge by local authorities.
Waters to be treated comprise mountain water and various waste waters.
In addition to general directives for discharge of waste water there are several
threshold values for specific parameters to be monitored in the field of tunnelling.
These parameters are listed in various regulations, e.g "General restrictions for waste
water emission to watercourses and public sewage systems" (Austria). Among these
parameters are:
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- pH-value from 6.5 to 8.5
- Filtratable substances < 50 mg/l
- Suspended solids < 0,3 ml/l
- Total organic carbon (TOC) < 5 mg/l
It is the function of a watercourse protection facility to reliably preserve these
criteria for discharge. The contribution of SEIBOLD-Messtechnik to this task is
the conceptual design, manufacture of the facility and service and support during
ongoing operation.
The challange of designing an easy to use and reliable concept is provision for
changes generated by the tunnelling operation and discrepancies from planning preconditions.
The simple construction supporting operational reliability is contrary to the
complexity of various other requirements.
Key factors of complexity typically are shortage of space, a small runoff ditch,
a long distance to tympanum and last but not least huge quantities of wast water.
The design model of an ideal watercourse protection faciliy by SEIBOLD-Messtechnik
provides distinct concepts and solutions for variable requirements.
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Key elements
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A typical watercourse protection facility comprises a settling installation for
pre-sedimentation at tympanum, equipment for flocculation, a settling installation including
oil seperation, a neutralisation unit and a device for final inspection. Of special
importance for unobstructed operation and proof of performance is online-measurement,
data recording and
telemetry.
Pre-sedimentation facility:
A settling pond for sedimentation of coarse solids in the waste water to be trated is
provided directly at the tympanum or, if applicable, in the tunnel. Coarse solids settled
in this settling pond will ease further treatment of waste water.
Flocculation:
In order to decrease exposure time in the settling pond and sedimentation of micro substances
(turbidity) the waste water is added flocculants.
Depending on geological conditions and with regard to structural engineering, anionic and
cationic flocculants based on polymer are used. These flocculants are carefully selected after
comprehensive testing and are reviewed within the scope of maintenance on a regular basis.
In numerous tunnelling projects SEIBOLD-Messtechnik has proven its specific expertise in
control of optimised quantity of flocculants subject to flow-rate and turbidity, as well
as an increase circulation of flocculants with the waste water to be treated.
Settling pond:
SEIBOLD-Messtechnik calculates dimensions required for the settling pond for sedimentation
based on the guidelines of SIA (Swiss Engineer- and Architect Association,
www.sia.ch).
As a rule of thumb (according to SIA standard 431) for 20 minutes of residence time within
the settling pond one can assume:
volume required for discharge (m3) = inflow (l/s) + 20%
surface required** (m2) ~ inflow (l/s) x 2 **for discharge into a river
Using scum boards of at least 50 cm depth buoying upwards of oil is kept back and drawn off
by the use of applicable pumps or skimmers.
Neutralisation:
pH-value of mountain water is alkaline due to chotcrete used for securing tunnelling.
Typically the pH-value is in the range of pH 10 (ascending tunnelling or using a
tunnel drilling machine, TDM) to pH 12 (descending tunnelling).
As a consequence of easy dosation and efficient dilution of CO2 in water, neutralisation by
means of CO2 addition is an inexpensive method and reliable in operation. Insertion and
circulation is provided by the use of static mixers of a diameter from DN50 to DN600.
Online-Measurement:
Parameters for the performance of neutralisation (flow-rate, p-values at inflow and drain)
and for sedimentation (turbidity and conductivity) are measured continuously. At the same
time these results of measurement are taken as parameters for control of neutralisation
and flocculation, as well as they provide the basis for reports to authorities and the
ordering parties.
Besides the various measurements already mentioned there are additional measurements to
be applied, e.g. temperature or nitrite, depending on the specific requirements of the
tunnelling project.
Data recording:
All results of measurement are stored on site as well as remote on a high-secure server
for further analysis and documentation purposes. Based on the information recorded not only
the performance of a facility is documentet completely, but also special events and
operating conditions can be monitored.
Telemetry:
Using GSM/GPRS technology allows for inexpensive transfer of all measurement results to a
high-secure server and further for optimising parameters for control of a facility in
cooperation with the operator. Please find further information on telemetry
here.
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Stationary equipment
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For flow-rates of more than 40 l/s, appropriate space for installation and a construction
period of more than two years, watercourse protection facilities based on earth-moving
construction are a proper method of application.
The level of all basins and inflows is planned in a way that no pumps are required
within the facility; waste water flows through the facility without intervention. In general
pumps in this context negatively impact performance of a facility by artificial variation
of inflow and further represents additional risk to reliability of operation.
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A stationary watercourse protection facility comprises a distribution basin, three settling
ponds, a basin for neutralisation and control pool. Inflow is carried out through the
distribution basin, where the following settling ponds can be filled by the use of sliders.
Two settling ponds are filled in parallel during normal operation and the third one is used
as flood detention basin in case of incidents and as evasion basin while clearing other
basins from sludge. 30 Minutes can be taken as reasonable time for retention, as whithin
this time troubleshooting in case of minor incidents is possible. Systems that in case of
incidents try to redirect waste water back to settling ponds are not being considered as
recommendable by us.
Discharge of the waste water is provided by means of an outlet shaft, directing the waste
water to a river or to a pump sump. Water quantity typically is measured by use of an
overfall weir, installed to the outlet shaft. Overfall weirs are robust, unproblematic to
use and long-lasting. Further we like overfall weirs due to the fact that in case of
power outage or failure of the supersonic sensor the quantity of water can easily be
measured by the use of a foot rule and then be recorded in the operating manual.
We offer all essemntial support to your watercourse protection facility, from the conceptual
design to the generation of plans for authorisation by local authorities, of course
manufacture of the facilities and maintenance. For setting up right dimensions our
calculations are based on standards of SIA (Schweizerischer Ingenieur- und Architektenverein).
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Mobile equipment
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For tunnelling projects where not enough space is available for setting up a stationary facility,
or due to a relatively short project time a stationary facility can not be installed in an economically
useful way, SEIBOLD-Messtechnik offers specifically equipped mobile facilities, providing all functionality
of typical watercourse protection facilities at minimum space.
Mobile watercourse protection facilities typically comprise a treatment- and a dry-part. Depending on the
flow-rate to be expected they are installed into 10- or 20-feet containers.
To the treatment part of the container measurement of flow-rate, measurement of pH-value at inflow and
all equipment required for adjusting the pH-value by the use of CO2 metered addition is installed.
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All hardware for measurement and control of the mobile facility can be found in the seperated dry-part
of the container, guaranteeing for the performance of the facility. Beyond this general equipment, each
container is prepared with various additional features, i.g. forklift-pocktes for easy transportation.
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SEIBOLD-Messtechnik und Projektentwicklug GmbH,
A-1110 Wien, Grillgasse 51
Tel +43 1 332 00 60, Fax +43 1 332 00 60 44,
office@seiboldme.com
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