sampling of wastewater - presto · sampling of wastewater ... constantly changing load in the...

Sampling of wastewater

Wolfgang Stump

Öko-control GmbH; Burgwall 13a;

D – 39128 Schönebeck

Telephone: +49 (0)3928/42738; Fax: 42739

E-Mail: [email protected]

Outline:

1.) Reasons for sampling of wastewater in a sewage treatment plant

2.) Reasons for sampling of wastewater in a sewer system

3.) Execution of the sampling of wastewater


Oily layer of scum on a secondary clarifier


Sampling of wastewater 1.) Reasons for sampling of wastewater in a sewage treatment plant

Operational problems in wastewater treatment plants:

Degenerated activated sludge, fungi or Microthrix under the microscope


bulking sludge and floating sludge (scum) in aeration and clarifier



Increased wear on aeration grids and membrane aeration



Limit exceeding by tensides or persistant pollutants in the effluent



Crystallizations in the pumps and pipes of sludge treatment


- Process monitoring

- Determination of the efficiency (cleaning capacity) of a wastewater

treatment plant and of individual process steps

- Specific questions and research in case of operational

malfunctions

- Identification of "illegal" indirect discharges into the sewer system

- Pollution load determination for indirect dischargers


Problems with waste water discharge:

Discharge of fat-containing wastewater or foam formation in sewage pumping

stations and shafts

Sampling of wastewater 2.) Reasons for sampling of wastewater in a sewer system


Oil disaster in the sewer network



Corrosion in sewage pumping stations due to high salt concentrations of a metal

plant



Floating solids from a plastic recycling plant


Problems in the WWTP inflow:

constantly changing load in the discharge of waste from the food industry (chocolate

factory, dairy); identifying surcharges for high-contaminators


Illegal discharges:

Sewage of a bread factory and compost leachate


Illegal discharges:

Wastewater of a printing plant and a grease recycling plant


Illegal discharges:

Waste water from the electroplating


There are basically only two types of sampling:

Right or wrong!

• Sampling is the first step of each analysis

• Error in sampling can not be compensated for later

• 90% of all erroneous results arise from errors in sampling

Sampling of wastewater 3.) Execution of the sampling of wastewater

Manual sampling:

• Single sample / sample

• one or multiple removal from a bulk

• Composite sample (average sample <= 2h)

• repeated extraction from a bulk over a period

• Combined samples consist of at least five samples, which

are taken in an interval of not less than 2 minutes, and over a

period of more than 2 hours

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Technique used:

Sample cup of glass or plastic (volume 0.2 - 1.0 l)

Sample container (about 10 liters) or homogenizer

Sample bottles (1 liter or larger), usually made of glass

Cooler with ice packs

Thermometer

Meter for on-site measurements

If necessary chemicals to stabilize


Combined sample in WWTP effluents


• Sampling location:

Manhole or open channel with a length of at least 1 - 2 m and a

depth of 15 - 20 cm.

• Implementation:

The sampling cup with the opening in the flow direction below

the water surface is moved at a speed matched to the flow.

To avoid contamination, the sampling cup may touch either

wall or bottom of the channel.

Between the sampling operations the sampling cup may not

be placed on the ground.

• Problems:

Low water, high flow rate, deep channels, floatables, backwater


- The samples must be transferred immediately to the laboratory.

- If immediate processing of the sample in not possible, the

samples must be preserved in accordance with the parameters to

be determined.

- The preservation of the sample has to be carried out directly

after collection.

- All chemicals used to preserve shall correspond the purity "for

analysis" (p.A.).

- During transport to the laboratory, the samples must be stored

at 4 °C and dark.


• Automatic sampling (continuous):

Single sample

Composite sample / average sample

2-h composite sample

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Limit value

Automatic sampling (discontiuous):

• Event sample

This kind of sampling is inter alia applied to document limit value exceedances of

wastewater relevant parameters. This sample mode is only activated when the

limit value is exceeded or a range is exceeded. Otherwise, the device is in "standby"

mode.


• Operating modes of the automatic sampling (discontinuous):

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Time-proportional sampling

Quantity-proportional sampling

Flow proportional sampling


• Devices for the automatic sampling

Mobile samplers for use in sewer system

Stationary samplers for use in wastewater treatment plants


• Devices for the automatic sampling

Technique used:

peristaltic pump or sampling control

Sample container is about 10 liters or homogenizer

Sample bottles 1 liter or larger, usually made of glass

Cooler with ice packs

Thermometer

Measuring devices for on-site measurements

If necessary chemicals for stabilization



• In wastewater treatment plants:

• before the treatment plant (inlet)

• after the treatment plant (outlet)

• between the various plant parts

• after the primary clarifier

• after the aeration tank

• before the denitrification tank



• In wastewater sewer system:

Explosion regulations!

Accident prevention regulations!


• Sampling with peristaltic pump (hose pump)

Suction (intake)

blow out and

backwash

Aspirate sample,

measure volume

and dose

Suction

(intake)

backwash



• Sampling with peristaltic pump (hose pump)

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1. Backwash 2. Suction / intake 3. Dose 4. Bottling


• Sampling with vacuum pump


• Sampling with vacuum pump

Sample preservation, transport and storage

- Most common method of preserving is cooling to a temperature between 0

C

and 4

C. Cooled and stored in the dark most of the samples are typically up to

24 stable.

- For some wastewater constituents long-term stability is achieved at -18

C.

- In case of composite samples for longer periods preservation should be part of

the of sampling.

- It may be necessary to use several samplers to investigate both conserved and

non-conserved samples.


Errors in sampling of wastewater

General:

- By confusing the sampling point the wrong sample is taken

- Confusion of samples due to poor labeling and incomplete or incorrectly completed

protocol

Contamination throug substances into the sample:

- Carryover of substances though unproperly flushed or cleaned equipment (including

hoses, riser pipes, wire ropes, cable feeds, etc) and sampling containers

- Contamination of the sample by use of incorrect sampling devices (eg abrasion of

materials, lubricants in pumps) or not appropriate tools (eg tapes)

- Risk of cross-contamination through chemical preservatives

- Mix-up of closures

- Use of not sufficiently purified utilities on site (pipettes, filtration devices, etc.)

- Contamination from the surrounding air



Losses due to discharge of substances from the sample:

Outgassing of volatile constituents by not keeping in gas-tight or not completely filled

containers.

- Loss of volatiles by incorrectly applied sampling technique (eg suction pump)

- Diffusion of sample ingredients into the sample container material

- Sorption of ingredients to tube and container walls

Changes due to chemical or biochemical reactions:

Oxidizing or reducing substances alter the concantration of certain parameters.

- Generation of precipitates can occur (precipitation)

- Bacterial activity can cause changes (eg ingredients can be consumed or be

converted into other compounds)



Sample bottles for waste water must not be

used for sludge samples.

Different bottle sets for different scan tasks at

hand.

The sample bottle used for the feed must not

be used for the discharge of a WWTP and vice

versa.


Backflow in the sewer system

Wastewater from a dairy flooded

and destroyed automatic samplers

in a shaft through backflow in the

sewer channel.



Security at sampling of waste water:

Accident prevention regulations and safety requirements must be observed!

Working in channels, pools, wells, pumping stations, water treatment plants:

Danger points to consider:

- Explosions due to explosive gas mixtures in the channel

- Poisoning by toxic gases (hydrogen sulfide, carbon monoxide)

- Suffocation due to oxygen deficiency

- Risk of epidemics by pathogenic germs

- Risk of injury from falling or slipping

- Danger of drowning

- Danger of falling objects



Tasks/work in enclosed space

Before an enclosed space (pumping station, calculating space emptied tank, pit, pit,

etc.) is entered - both in the upper as well as in the lower part:

-Testing for Explosive

- Testing for the presence of H2S and CO and other toxic gases

- Testing for the presence of a sufficient concentration of oxygen (> 20%)

Furthermore:

- Wear full emergency equipment, direct contact to waiting helpers

- Appropriate protective clothing

- Air testing devices, leave location in case of risk

- Specific hygiene requirements

Vaccinations and Traffic safety


Sample identification and protocol

The sampling protocol should include the following information:

- sampling location,

- date, time, beginning and end of sampling,

- duration of sampling,

- purpose of the sampling,

- details of sampling procedures,

- details of the on-site analysis,

- name and signature of the sampler

As "Notes", all characteristics of the sampling site and the sampling shpould be

listed. Also preservation, storage conditions, control samples from other institutions,

the presence of witnesses, nature, origin and quantity of released hazardous

substances, possibly injured people.


An immediate transfer of the samples to

the qualified laboratory prevents errors,

losses and additional effort by

conservation.


Thank you for your attention and I look forward to your questions.

Wolfgang Stump

Öko-control GmbH Schönebeck

03928/42738

Sampling of wastewater 4.) Conclusion and Summary

sampling of wastewater - presto · sampling of wastewater ... constantly changing load in the...

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