Sludge

Bucher Piston Presses

Bucher presses are the only mechanical devices on the market that enable the dewatering of sewage sludge the limit of their physical dehydrability and therefore belong to the group of the most effective dewatering devices.

In practice, a higher level of sewage sludge dewatering is only possible with prior application of sludge disintegration or hydrolysis. The example of many implementations confirmed by references shows that the technical service life of Bucher piston presses is over forty years.

The manufacturer of the presses is the company Bucher Unipektin AG from Switzerland, and Proffico is their exclusive distributor in Poland for the municipal and industrial sectors. The first investments in Poland in the field of sewage sludge dewatering using Bucher piston presses were installations in Radom and Puławy, and currently piston presses are also operating in Rzeszów, Lubartów and Józefów.

Principle of operation of piston presses

The main element of the press is a cylinder and piston. Between the piston and the cylinder, special drains are placed, which discharge the filtrate to the sewage system. The mixture of sediments with flocculant is fed to the cylinder using a screw pump, filling the free space between the drains. The size of the cylinder and the number of drains (including the filtration surface) determine the efficiency of the press.
The operating principle is identical to that of piston engines, where cyclic compression and expansion phases occur, with the difference that the piston with the cylinder additionally rotates around its own axis at a speed of approx. 6 revolutions per minute and the empty space in the cylinder is filled with sediments. The drains have been designed so that during pressing (compression) they press into the sediment, thus removing excess effluent. Each drain consists of a grooved core made of polyurethane, with a filter fabric pushed on, through which the effluent from the sediments flows away.

Peripherals and Controls

The sludge from the storage tank is fed to the press using screw pump. During pumping, the sediments are mixed with a flocculant solution using a special dynamic mixer. Each drainage installation is equipped with microwave dry mass measurement, thanks to which the flocculant dosage occurs solely as a function of dry mass and flow. This solution effectively eliminates the phenomenon of polymer overdose.

The sludge and flocculant pipelines are fitted with flow meters, giving real indications of the flow of both media.

The press is equipped with power supply system with control, which cooperates with the main electrical switchboard of the entire sludge dewatering installation. An interesting feature not found in other technologies is the continuous monitoring of the average dry mass of sludge during the dewatering process. The press also has a control panel that provides full insight into the data - both current and archived, and allows control of the device.

Operational aspects

Effects of dehydration – Bucher piston presses were tested in several sewage sludge disintegration systems achieving results ranging from 45 to 50% dry matter, and in the case of one of the new technologies, a dewatering degree of up to 70% dry matter was achieved. It is worth noting that such dewatering effects are no longer possible on classic devices such as belt presses or centrifuges.

Electricity consumption -Bucher piston presses, due to their hydraulic operating principle, belong to the group of energy-saving devices. In relation to the energy consumption of the entire sludge dewatering installation in Bucher presses, the indicator expressed in [Wh/kg H₂ABOUT] is already in the range of 1.5 to 2 [Wh/kg H₂O]. This result places Bucher presses in the top tier.

Chemical consumption – flocculant and coagulant consumption is comparable to other methods and is usually around 6-16 kg AS/t DM of sludge. The exact consumption value is determined at the pilot test stage or during the start-up of the installation.

Effluent - Due to the principle of operation, Bucher piston presses are characterized by the cleanest effluent of all available dewatering methods. Usually, the suspended solids in the effluent do not exceed 100 mg/l.

Odors – the Bucher piston press, due to its specificity, does not cause significant emission of odours to the environment. The press is hermetically closed during the full filling, expansion and squeezing cycle, opening only for 8 minutes in the unloading phase. In this case, the sludge does not emit odours, because after dewatering in the piston press it has a loose form with a slightly earthy smell.

Noise – Bucher piston press produces noise emissions below 85 dB during operation. This value is acceptable for the staff and does not cause excessive nuisance (this range is comparable to loud music and street traffic).

Strengths and weaknesses of Bucher presses

The use of Bucher piston presses, in relation to typical methods of sewage sludge dewatering, has the following advantages: advantages:

dewatering of sludge to the limits of physical possibility;
over 40 years of technical life of the device;
low energy consumption (up to 2 Wh/kg H₂ABOUT);
no odor emissions (closed system);
high quality of effluent (suspension level up to 100 mg/l);
process flexibility;
process control by continuous measurement of the degree of dehydration;
automatic cleaning of the filter fabric due to the generation of countercurrent air flow during piston retraction;
simplicity of maintenance generating low costs for repair and maintenance works.

Drawback Bucher presses are its dimensions and relatively high investment costs, which are a barrier for some users, especially smaller treatment plants. In addition, Bucher presses require qualified personnel to operate them, a stable flocculation process and a feed at a level above 2% sm. Based on experience from the implementation of installations in Radom and Puławy, it can also be stated that Bucher presses accept only correct sludge transport systems. After dewatering in the press, the sludge has the form of loose soil in the form of small granules, therefore, in order to ensure their correct transport, the filling factor of the screw conveyors should not exceed 30%.

more information can be found in the pdf file.