Page 36 - trends in automation 1.2013

W

astewater treatment plants

don’t just have to deal with

household and industrial

wastewater. Rainwater also

enters the cleaning process via the sewer

system. Because wastewater treatment

plants are designed to cope with a certain

load, just like manufacturing plants,

above-average rainfall tends to push them

to their limits. Stormwater retention

tanks are the solution. They collect the

excess water from the sewer system

and thus relieve pressure on wastewater

treatment plants and the natural body

of water. There is, however, one problem –

stormwater retention tanks are often

located in remote areas where there is

no regular power supply. These facilities

therefore cannot be automated and

employees must actuate gate valves

manually, which takes up valuable time.

Sophisticated monitoring

The management of stormwater retention

tanks is a constant challenge for the

Abwasserverband Weißach und Oberes

Saalbachtal. Wastewater from 22 mu-

nicipalities enters the central wastewater

treatment plant at Heidelsheim. Every

time it rains, all 39 local stormwater reten-

tion tanks should, strictly speaking, be

checked. This is a difficult task, particular-

ly during prolonged spells of wet weather.

Furthermore, during the cold months of

the year there can sometimes be complica-

tions with the electrically actuated exhaust

flow control valves that control the flow

of wastewater into the sewer system. The

electric spindle drive soon reaches its per-

formance limits when the butterfly valves

are frozen. Both of these problems were

discussed when a Festo field sales repre-

sentative came to visit, and this paved the

way for a forward-looking project.

An energy self-sufficient solution

Back in Esslingen, the discussion with

the field sales representative led to

the drafting of a research paper, which

examined the available options and

their feasibility. A practical concept was

created as part of an undergraduate thesis

and this resulted in a forward-looking

complete solution for the energy self-suffi-

cient automated and remote-controlled

handling of gate valve actuators. Shortly

afterwards, an initial pilot project was

set up with the Abwasserverband Weißach

und Oberes Saalbachtal. Solar energy

harvested using photovoltaics is used to

power the control unit and operate the

pneumatic actuators type DLP. If there is

an extended power failure, an integrated

emergency operation function allows

the process valves to be actuated several

times. The plant can continue to operate

for around a week even in bad weather.

A GSM modem forwards all the relevant

data to the wastewater treatment plant’s

control centre simultaneously. From

here, the gate valves can be closed and

opened centrally. As an extra safeguard

and to ensure shorter response times

in the event of malfunctions, the respon-

sible Festo employee is also notified.

High rainfall levels are overloading many wastewater treatment plants.

Stormwater

retention tanks can prevent this from happening. An energy self-sufficient, automated

control system with pneumatic actuators from Festo ensures greater reliability and

lower costs. It has proven to be a major success in a pilot project.

Rain under

control

Energy self-sufficient automation of wastewater technology