Autosamplers
Autosamplers – samplers are used for automatic collection of sewage samples in order to test their quality. Collection can be carried out proportionally to time, sample volume or flow.
Municipal and industrial sewage tests are performed in accordance with the regulations:- Regulation of the Minister of Maritime Economy and Inland Navigation of 12 July 2019 on substances particularly harmful to the aquatic environment and the conditions that must be met when introducing sewage into water or soil, as well as when discharging rainwater or meltwater into water or water facilities (Journal of Laws 2019, item 1311),
- Regulation of the Minister of Maritime Economy and Inland Navigation of 28 June 2019 on substances particularly harmful to the aquatic environment, the introduction of which in industrial sewage to sewage facilities requires a water permit (Journal of Laws 2019, item 1220),
- Regulation of the Minister of Construction of 14 July 2006 on the method of fulfilling the obligations of suppliers of industrial sewage and the conditions for introducing sewage into sewage facilities (Journal of Laws 2006, item 136, 964).
- Sample dosing
- Pump type
- Sample storage
- Construction
- Place of application
SAMPLE DOSING - DIRECT AND INDIRECT
The wastewater samples that go into the containers should be representative, which means that they should not mix. Autosampler manufacturers offer solutions based on a wheel feeder, a wheel feeder with an intermediate tray, and an XY feeder. A wheel feeder is a simpler and cheaper solution - the feeder arm moves around a set circle. The limitation is the need to use an intermediate tray, which allows the wastewater samples to be delivered to places other than those resulting from the circular movement of the feeder. In the case of a change in the size of the bottles, it is also necessary to replace the intermediate tray.
The XY dispenser does not have such limitations. In this case, samples can be delivered to any place in the chamber and the use of an intermediate tray is completely unnecessary. Direct dispensing in the XY system is a more expensive solution, but allows for greater flexibility in terms of bottle configuration and size.
The circular dispenser with an intermediate tray requires periodic cleaning of the tray (removal and washing) and is characterized by an increased risk of mixing wastewater samples from different collection times.
Two types of pumps are used in autosamplers: vacuum and peristaltic.
Peristaltic pumps, due to their design, enable direct collection of appropriate sewage samples in proportion to the flow. The disadvantage of peristaltic pumps is their high sensitivity to contaminants present in sewage. Solids can block the flow through the tube, and the diameter of the tube can also decrease due to the fouling of its walls. In such a case, the peristaltic pump does not work properly and may not even collect a sewage sample. This is because the pump only counts the revolutions performed, not controlling the actual flow. Therefore, a "fictitious" flow and "fictitious" sampling can occur. This type of pump is therefore dedicated to purified sewage, e.g. at the outlet of a treatment plant.
Vacuum pumps measure the amount of liquid based on a quantity sensor, which always corresponds to the "real" flow. Vacuum pumps are much more resistant to contamination and are therefore dedicated to collecting sewage at the inlet to the treatment plant and at the collection stations for delivered sewage. Vacuum pumps are more expensive than peristaltic pumps.
SAMPLE STORAGE TEMPERATURE - ACTIVE AND PASSIVE COOLING
During collection, samples should be stored at a temperature of 0aboutC to 4aboutC. This means that an active cooling system must be used in the sample storage chamber, operating 24 hours a day. In the case of stationary autosamplers, this is not a problem due to the use of mains power. In the case of portable autosamplers, it is necessary to use an efficient cooling system, very good thermal insulation and a power supply based on capacious batteries. Most manufacturers cannot cope with such requirements. Practically all portable autosamplers available on the market have only "passive" cooling in the form of cartridges. Theoretically, the fluid cooled in the cartridges is supposed to take over the excess heat brought to the sample chamber from the external environment. In the case when the ambient temperature exceeds the assumed upper limit of 4aboutC after less than an hour the sample storage chamber overheats. When the temperature in the chamber exceeds 4aboutC one of the requirements of accredited wastewater measurement is not met. In turn, non-accredited measurement cannot be used in formal and legal situations but only for own, internal analyses.
DURABLE STAINLESS STEEL HOUSING
Samplers often operate in open spaces, where they are exposed to rain, sun, low and high temperatures. The practice of using autosamplers in the field indicates that these factors have a negative impact on the materials from which they are made - this is particularly true for plastics, which are subject to a natural "aging" process under the influence of solar radiation and temperature. At low temperatures, plastics become more brittle and susceptible to damage from accidental impact. However, plastic housings are cheaper to produce and allow for more free forming of their shape. Regardless of the declarations made by autosampler manufacturers about the equivalence of the features of plastic and stainless steel, devices with stainless steel housings always exceed the durability of those made of plastic.
SEPARATION OF SAMPLING CHAMBER FROM ELECTRONICS
It is rational from the technical point of view and the safety and durability of the autosampler to completely separate the chamber in which the collected and stored sewage is located from the chamber with electronics and control. Such a separation guarantees that even in the event of an accidental leak in the hydraulic system, the sampler electronics will not be flooded and destroyed. Of course, for safety reasons, the control chamber should be located above the sampling chamber.
APPLICATION PLACE - STATIONARY AND PORTABLE MODEL
Stationary autosamplers are usually placed at the inlet and outlet of sewage treatment plants or at collection stations. Portable autosamplers are used for control measurements in the case of settlements with external entities and for temporary measurements in locations normally serviced by stationary autosamplers. They offer solutions based on a wheel feeder, a wheel feeder with an intermediate tray and a feeder in the XY system. A wheel feeder is a simpler and cheaper solution - the feeder arm moves around a set circle. The limitation is the need to use an intermediate tray, which allows the sewage samples to be delivered to other places than those resulting from the circular movement of the feeder. In the case of a change in the size of the bottles, it is also necessary to replace the intermediate tray.