De nutrifier - Lenntech

De-nutrifier

1 System introduction

Waterships and other authorities responsible for the quality of the surface water currently set rigid effluent discharge limits on total phosphor and total nitrogen besides the traditional COD, BOD, TKN and TSS* requirements, to stop the ongoing eutrophication.

Formerly intensive aeration to purify the wastewater was sufficient, with little nutrient removal as a result. However newly constructed waste water treatment systems should now include anoxic and anaerobic compartments to achieve biological phosphates and nitrogen removal.

For the removal of nutrients (phosphor and nitrogen) from the wastewater, BOD (as a carbon source) is required. Optimal biological removal efficiency will be obtained when treatment steps with carbon removal without phosphates and nitrogen removal are avoided.

The De-nutrifier consists of a low loaded activated sludge system with a four rings reactor without preliminary clarification and without sludge fermentation. Nutrients removal prior to carbon removal is the principal design criterion of the De-nutrifier.

The second pillar of the system design is the utilization of all rest heat on behalf of the biological reactions in the activated sludge. The application of a Regul-air cover on the activated sludge reactor retains heat in the system. Furthermore, heat from the sludge treatment can be brought into the activated sludge reactor. These innovative measures result in a temperature increase in the reactor and this will subsequently result in a significant increase in the biological activity of the activated sludge and the performance of the system.
The Regul-air cover is combined with an integrated biofilter to reduce aerosols and stench emissions, to a negligible level.

2 The development of the De-nutrifier

In order to purify the wastewater up to required phosphates and nitrogen effluent limits, the following system choices are made:
1 No primary clarifier will be applied in order to avoid the removal of carbon by settling without significant removal of phosphor and nitrogen.

2 The system consists of a low loaded activated sludge reactor with four compartments: a selector for optimal sludge loading and settling characteristics, an anaerobic compartment for biological de-phosphatation, an anoxic compartment for de-nitrification and an aerobic compartment equipped with aeration devices for nitrification and carbon removal.

3 No sludge digestion will be applied to avoid extra nutrient loading of the activated sludge reactor. The supernatant discharged from the sludge digestion contains high amounts of phosphor and nitrogen. A sludge handling without nutrient release will be applied.

4 The system will be completely covered and insulated. The Regul-air cover will be equipped with a conditioner to control the release of air blown into the aerobic compartment. The result will be an optimal utilisation of the rest heat set free by the system devices during winter and control of temperature in the system through forced air transmission during summer. The air is emitted by way of a stack after aerosols and stench are removed in a biofilter.

3) Types of wastewater suitable for the De-nutrifier

The De-nutrifier is designed to purify the wastewater with a high nutrients (nitrogen and phosphor compounds) concentration and to purify the wastewater from which the effluent concentration has to meet rigid discharge requirements regarding the total phosphor and the total nitrogen concentrations. Waterships and other authorities responsible for the quality of the surface water in the northern EU member states require maximum effluent discharge concentrations of 1 to 2 mg/l phosphor and 5 to 10 mg/l nitrogen in the battle against the ongoing eutrophication.

The nutrients removal efficiency of the aerobic sewage purification systems is so small that the effluent discharged by these systems does not meet the required phosphor and nitrogen effluent concentrations. The De-nutrifier is an obvious system to be recommended in cases of extensions, replacement and new constructions of sewage treatment utilities.

Many industries, in particular potato processing facilities, breweries, sugar production and sacharose or glucose processing facilities, produce wastewater’s with high nutrient concentrations when anaerobically pre-treatment devices are provided. The De-nutrifier is recommended for the final treatment of these pre-treated wastewater.

4) Advantages of the De-nutrifier compared to aerobic systems

The De-nutrifier in combination with the described pre-treatment, post-treatment and sludge treatment has the following advantages compared to the traditional aerobic systems.

1) The De-nutrifier has been designed for maximum phosphor and nitrogen
compounds removal by means of anaerobic and anoxic compartments. In conventional activated sludge systems nitrogen and phosphor are only partly removed. Furthermore, the nutrient removal can be exactly controlled by controlling the different recirculation flows.

2) Due to the Regul-air cover on top of the reactor and a controlled air release from the Regul-air cover, the temperature in the system will be increased and consequently, the volume of the reactor can be significantly reduced.

3) The De-nutrifier is a compact reactor covering a small site surface. The four treatment steps are integrated in one reactor. The total reactor volume is reduces because of the increased process temperature in the reactor. Furthermore the required surface for the system is reduced because of the relative high (6-8m) water level in the reactor;

4) By means of blowers and bottom aerators the aerobic compartment of the De-nutrifier is aerated and mixed. The air that is brought into the reactor at the bottom will be collected underneath the Regul-air cover. The relative warm air under the cover, under slightly increased pressure will greatly reduce the heat losses from the reactor during wintertime and therefore result in a increased temperature in the sludge liquid mixture.

5) The air that is withdrawn from the Regul-air cover is cleaned in a biofilter and subsequently discharged by using a high stack to reduce the emission of aerosols, pathogens and stench so that the immission levels can be neglected outside the borders of the site;

6) In the post-treatment chemical/physical déphosphatation will be applied consisting of a flocculation filter. Addition of Al(OH)3 followed by AlCl3 produced from waste streams is recommended because the costs of these agents are lower than the price of the traditional agents and because the de-phosphatation performance is better;

7) Rapid sludge dewatering in the sludge thickener can be obtained by using a turbity level controlled dewatering pump. The dry matter concentration in the sludge can be raised to 4,5 %. The thickened sludge will be subsequently pre-heated using the rest heat of the own combined power-heat station up to 70oC and will be dewatered in centrifuges upto 27% dry matter;

8) Own power supply by means of a combined power heat station equipped with a de-NOx installation is recommended. The rest heat will be used for drying of the sludge and raising the temperature in the reactor;

9) After dewatering in a centrifuge the sludge is dried in a sludge drying unit increasing the dry matter upto 80% - 95%, depending on the type of sludge. The heat (energy) of this unit will be supplied by the power-heat station;

10) There is a market for the sales of granulated sludge as fertiliser for agricultural purposes or as fuel for cement and steel production facilities. The current price amounts to 23 Euro/ton for the dried granulates;

11) The investment costs of the De-nutrifier are significant lower than the investment costs in a traditional aerobic wastewater purification system while the total performance of the system is higher, especially with regards to nutrient removal. The reactor can also be designed smaller due to the increase of temperature of the system, which reduced the investment costs.

12) The operational costs of the De-nutrifier are significant lower than the operational costs in a traditional aerobic wastewater purification system because of the use of rest heat in the system, the reduced use of chemicals in the system, the low sludge treatment costs and the revenues of sales of dried sludge granules;

13) The productivity of the De-nutrifier given as the Internal Rate of Return on investment is high compared to traditional aerobic wastewater purification systems.

5) Product and process guarantee

The De-nutrifier is constructed under the product guarantee for all system devices and for the system as a whole for a period of time at least equal to the term of the lease contract made up for the design build project realisation.

The process guarantee includes a performance bond regarding the COD and TSS removal efficiencies can be provided in the framework of the design build contract of the De-nutrifier.

After the provision of the product guarantee and the performance bond the operational costs and revenues have been safe guarded. Therefore the return on net revenues of the department of the enterprise that installed the De-nutrifier will be guaranteed.