FAQ EloVac®-P/EloVac®

Data and dimensions

What is the difference between EloVac® and EloVac®-P?

EloVac® is a technology for vacuum degassing of digested sludge. EloVac®-P is an add-on for EloVac® which facilitates simultaneous phosphate precipitation with vacuum degassing.

Where is EloVac® applicable?

EloVac® is applicable at all WWTPs with anaerobic digestion that are interested in an improvement of their carbon footprint and improvement of the dewaterability of the digested sludge.

Where is EloVac®-P applicable?

EloVac®-P is also applicable at all WWTPs with anaerobic digestion that are interested in an improvement of their carbon footprint. With the additional phosphate precipitation EloVac®-P is beneficial at WWTPs with elevated phosphate concentration. These are typically observed at Bio-P plants, WWTPS with high strength waste with high phosphate content, advanced digestion plants or sludge treatment centers. Also at treatment plants with struvite scaling issues EloVac®-P is beneficial to apply.

What is the minimal and maximal size of a WWTP to apply EloVac®?

From a technical perspective there is no limitation to the application of EloVac® in terms of the treatment plant size. An economic application of EloVac® is expected at WWTPs sizes from ca. 30,000 PE depending on several factors like the disposal costs. There is no upper limit for the application. Currently our biggest EloVac® unit can treat 50 m³/h. At WWTPS with a higher sludge flow parallel units will be installed.

Is there a minimum concentration of phosphate to apply EloVac®-P?

We recommend a minimum PO4-P concentration of 50 mg/l for the application of EloVac®-P.

What are the available sizes of EloVac®?

There are standard units available with a treatment capacity of 10 to 50 m³/h.

What are the space requirements for EloVac®?

The smallest unit (EloVac® 10) has a footprint of ca. 1.8 x 5.5 m. The biggest unit (EloVac® 50) has a footprint of ca. 4.9 x 6.1 m.

Can EloVac® be placed outside a building?

EloVac® is a completely skid mounted. The skid can be either placed inside of a building or alternatively in a container.

What materials are used for the construction of the EloVac®?

The main parts are made of stainless steel.

Which standards are used for the application of EloVac®?

EloVac® is available based on European standards or US standards. Other standards are available upon request.

Is it possible to evaluate the effects of EloVac®/EloVac®-P on labscale?

Yes, we can offer lab tests to determine the amount of vacuumed gas which can be expected. Additionally, the effect of EloVac® or EloVac®-P on several parameters like the pH, the density, the phosphate concentration and the dewaterability can be evaluated. Also the specific required Mg-dosing quantity can be assessed.

Is it possible to pilot EloVac®?

Yes we can offer a pilot plant with maximum treatment capacity of 20 m³/h. The recommended time of the pilot on site is 1 - 3 months.

What is the typical delivery time?

The delivery time is 3 – 5 moths.

Maintenance

What are the typical maintenance works?

The reactor itself is maintenance free. An inspection is recommended every year. The progressive cavity pumps require typically change of stator and rotor every year. PH probes have to be maintained every 1 – 2 weeks.

What kind of spare parts are needed for EloVac® skid?

Maintenance skids for the progressive cavity pumps (feed pump, effluent pump) and the vacuum pump are recommended. Also a spare pH probe is recommended. All the equipment is standard equipment and spare parts are very quickly available.

What is the typical weekly time requirement for the wwtp personnel?

On average 2 hours per week are required for visual inspection, analytics (ortho-phosphate measurement), maintenance of pH probe (every 1 – 2 weeks) and progressive cavity pumps (typically every year).

Does P-precipitation within EloVac® cause problems within the dewatering machine?

Due to the fact that there is no crystal growth in the EloVac®-P degassing reactor the precipitated struvite crystals stay very small. Hence, the micro-crystals don’t cause wear and tear on the dewatering machine.

Can EloVac® be applied with thermophilic sludge?

Yes.

Can EloVac® be applied with advanced digestion?

Yes. Due to the higher specific gas yield and related higher amount of entrapped gas bubbles in the digested sludge EloVac® is especially beneficial at sites with advanced digestion. Advanced digestion in general causes a higher P-release. The elevated Phosphate concentration in the sludge often leads to uncontrolled struvite scaling issues. This can be prevented by EloVac®-P.

How much gas is expected to be vacuumed from the sludge?

The amount of vacuumed gas is dependent on the digestion process itself and the viscosity of the sludge, i.e. in advanced digestion processes higher amounts of vacuumed gas can be anticipated. Depending on the specific conditions the gas amount is 200 – 600 L/t of sludge.

Does EloVac®-P affect land application of the dewatered sludge?

With EloVac®-P we don’t pursue a separation of the struvite crystals from the sludge but the struvite micro crystals stay in the digested sludge. Struvite is a slow release fertilizer with almost 100% plant availability of the phosphorous. Therefore, EloVac®-P even improves the fertilizer quality of the biosolids cake which makes it especially suitable for land application.

Operation

What is the typical timeframe for the installation and commissioning?

For a typical installation of an EloVac® 20 (throughput 20 m³/h) including commissioning, startup and operator training ca. 3 – 4 weeks are required.

How is EloVac® connected to the process?

In standard application EloVac® is placed directly after the digester, upstream sludge storage and dewatering machine. The vacuumed gas pipeline is connected to the biogas system.

What media are necessary to operate EloVac®?

To operate EloVac® only process water is required. For the operation as EloVac®-P (i.e. with simultaneous phosphate precipitation) Magnesium chloride solution (30%) is required.

How is the process controlled?

The process is controlled via a PLC with HMI.

What is the maximum dry solids concentration is the sludge feed to EloVac®?

The maximum recommended dry solids concentration is 5% DS. Higher dry solids concentration upon request.

What is the methane concentration in the vacuumed gas?

Depending on the amount of entrapped gas bubbles the methane concentration can be even more than 50%.

Can the vacuumed gas be utilised in a CHP?

Yes. The vacuumed gas is provided to the gas system of the WWTP and can be utilised together with the generated biogas in a CHP.

What effects on the dewatering can be expected with EloVac® or EloVac®-P?

Vacuum degassing has a positive effect on the dewaterability of the digested sludge. Based on our experience an improvement of 1 – 3%points can be expected with EloVac®. In case of an elevated phosphate concentration with simultaneous Phoshate precipitation (EloVac®-P) an improvement of the dewaterability of up to 5 %-points can be expected. Additionally, a lower polymer consumption is anticipated.

Can EloVac® contribute to the Carbon Footprint goals of a WWTP?

A study by Gärtner 2017 shows that on average direct GHG emissions of 11.6 kg eCO2 / PE can be expected from a WWTP. On the other hand, the average energy consumption of all wastewater treatment plants (reference Baden-Württemberg) is 33.2 kWh / PE * a. In the German electricity mix, this corresponds to a CO2 emission of 16.23 kg CO2 / PE * a. Considering that at present 17.5 kWh / PE * a are produced from regenerative energies on the WWTP (see 45. Leistungsvergleich der kommunalen Kläranlagen in Baden-Württemberg, Tobias Morck, und Gert Schwentner, DWA-Landesverband BW Stuttgart), remaining 15.7 kWh / PE* a with CO2 emissions of only 7.7 kg CO2 / PE * a. That means these CO2 emissions related to the energy consumption are even a smaller burden than the direct emissions. For this reason EloVac can really contribute significantly in reducing the overall carbon footprint of a wwtp.

What is the typical pH increase in the EloVac®?

The typical pH increase is 0.3 to 0.5 pH units.

Which configurations are possible for the application of EloVac®?

In the standard configuration EloVac® is installed between the digester and the dewatering. Another option is to install EloVac® in a loop configuration with the digester. This is especially beneficial for advanced digestion with high solids load, high specific gas production and a related decreased density in the digester.

What is the typical electrical energy demand?

The typical electrical energy demand for an EloVac® 20 (20 m³/h throuput) is ca. 10 kW. However, with the utilisation of the vacuumed gas EloVac® is operated energy positively.

Is foaming a problem inside EloVac®? If yes, how to address it?

Foaming has never been a problem so far. In any case there is a foam detection system and a spraying system inside the reactor tank which can spray water or anti foam agent if foam is detected.

How to address redundancy concerns with EloVac®?

The modular design of EloVac® helps to address redundancy concerns. If full redundancy is required, a second module has to be installed. Redundancy concerns can also be addressed by an optional delivery of the main pumps and parts as spares.

Is pre-equalisation necessary before EloVac®?

In general no, the digester upstream of the EloVac® works as equalisation tank.

Any sludge pre-treatment like screening, grit removal that may be necessary prior to EloVac® to prevent O&M issues?

For any kind of sludge treatment upstream grit removal etc. helps to minimize O&M issues. Of course, same applies for EloVac®

Is P-recovery possible with EloVac®-P ?

With EloVac®-P we don’t pursue P-recovery in the sense of separating the struvite crystals from the sludge. However, if the dewatered biosolids cake which contains the highly plant available struvite micro crystals is land applied this is a direct recovery route.

Can EloVac® be used on sidestreams?

In general EloVac®® can be used for all kind of liquids with a viscosity < approx. 100 mPas.

Safety

Are there any special requirements in terms of Ex-protection?

The inner part of the vacuum pump is rated as ATEX 0. The vacuum pump itself is mounted in a ventilated housing. The ventilation is controlled. If the ventilation fails all electrical equipment is switched of and the equipment is transferred into a safe mode. Therefore, in general there is no ATEX classification of the room where EloVac® is installed required.

Does EloVac® require a separate Ex room?

National requirements are different concerning the depending requirements. Please reach out to your local supplier for more information.