NL2023573B1

NL2023573B1 - Production of fatty acids from a sieve fraction of activated sludge from treated wastewater

Info

Publication number: NL2023573B1
Application number: NL2023573A
Authority: NL
Inventors: Theodorus Wilhelminus Maria Hendriks Antonius; Oosterhuis Mathijs
Original assignee: Haskoningdhv Nederland Bv
Priority date: 2019-07-26
Filing date: 2019-07-26
Publication date: 2021-02-18
Also published as: WO2021020964A1; EP3999653A1

Abstract

The invention is in the field of wastewater treatment, in particular to a method of producing fatty acids from a sieve fraction of waste water or activated sludge from treated wastewater, and is applicable to a filter fraction from any 5 aqueous solution comprising biological and/or organic mate— rial. The invention further improves removal of P and/or N in a water treatment installation.

Description

Production of fatty acids from a sieve fraction of activated sludge from treated wastewater

FIELD OF THE INVENTION The invention is in the field of wastewater treatment, in particular to a method of producing fatty acids from a sieve fraction of waste water or activated sludge from treated wastewater, and is applicable to a filter fraction from any aqueous solution comprising biological and/or organic mate- rial. The invention further improves removal of P and/or N in a water treatment installation.

BACKGROUND OF THE INVENTION The invention is in the field of wastewater treatment. Wastewater treatment typically involves several stages. During primary treatment, heavy solids may settle on the bottom of a basin and light oily materials may accumulate on the surface of the water. Heavy solids and light oils may be removed and the primary-treated wastewater may be subjected to a secondary treatment, wherein dissolved and suspended biological material may be removed. Secondary treatment may typically be performed using microorganisms that convert biological material being present into sludge. Typically, secondary treatment may in- clude also the removal of pollutants such as phosphates and nitrates and may be combined with a tertiary treatment to fur- ther polish the obtained treated wastewater quality. Secondary treatment of wastewater typically involves an anaerobic zone, an anoxic zone, and an aerobic zone, wherein wastewater is contacted with active sludge. The micro-organisms present in the sludge effectuate sludge growth, wherein organic matter is converted into sludge. Surplus sludge may be separated from the treated water by settlement and subsequently discharged from the wastewater treatment plant as waste. Recent improve- ments however, have managed to use the sludge as a valuable resource.

When treating wastewater, or likewise an aqueous solu- tion, typically a filter fraction remains. This filter frac- tion can be extracted from waste water, or active sludge, us- ing a screen filter, fine sieve, sieve drum, sieve bend or an- other sieve type. This filter fraction has in most cases a high organic matter content (around 90-95%), usually contains a lot of cellulose (> 30% of the organic matter), and is often easy to dehydrate to around 30-40% DS without using polymers.

There are major drawbacks of the prior art treatment. For instance the desired P removal cannot be achieved with only biological P removal and therefore additional chemical P re- moval is applied. This results in high costs on the one hand for the purchase of metal salts and on the other for the dis- posal of the chemical sludge formed. Also denitrification is now often relatively slow due to the presence of slowly de- gradable organic material.

The present invention therefore relates to an improved method of operating a water treatment system, which overcome one or more of the above disadvantages, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION The present invention relates in a first aspect to a method of producing fatty acids, comprising obtaining a filter fraction from an aqueous solution comprising biological mate- rial, the filter fraction may comprise >20 wt.% dry solids, such as 30-35 wt.%, the dry solids comprising >50 wt.% or- ganic material, preferably > 80 wt.®, such as > 90 wt.3 (wherein the wt.% is based on the dry solids content), and likewise the organic material being a source of convertible carbon, acidifying the filter fraction under anaercbic condi- tions by microorganisms, and by producing fatty acids. It is found that by increasing the amount of available fatty acids, the amount of biological P removal can also be increased; also the denitrification rate is increased and thereby the required purification volume reduced. It has been found that acidifying the filter fraction is possible under anaerobic conditions, the process conditions being controlled, for instance such that a pH is maintained between 5.5 and 6.5, preferably around pH=6; a residence time is sufficiently short to prevent the growth of (aceticlastic) methane formers as much as possible, and to keep acidifiers in the reactor (typically approximately 6 days residence time, depending on temperature); sulfate re- duction is prevented as much as possible; the fatty acid con- tent remains low, such as <40 g/l to prevent product inhibi- tion (too high fatty acid levels have an inhibitory effect on the conversion). The amount of filter fraction in the reactor may be varied, also in this respect, between 0.5-50 grams dry solids/l, preferably between 1-30 grams dry solids/l, more preferably between 2-20 grams dry solids/l, such as between preferably between 3-10 grams dry solids/1. It is found that under such conditions the organic material is converted into fatty acids as much as possible. Typically mainly acetate and propionate are produced, such as 30-70% acetate and 20-60% propionate, preferably 40-60% acetate and 30-40% propionate, based on a total amount of fatty acids. The fatty acids pro- duced can be used for improvement of biological P removal on a wastewater treatment plant (WWTP) with bio-P configuration, acceleration of denitrification in a WWTP is achieved, and production of bioplastics (PHA) is made possible, typically elsewhere. It is noted that the use of the fatty acids for the P and N removal is attractive because it can save on process additives, such as iron chloride or C-source. The total sludge production may decrease due to the present method.

The organic biological material often originates from cel- lulose or residues thereof, and often 50-80 wt.% of the or- ganic material originates therefrom.

Separation of the fatty acids and unconverted filter frac- tion may be done with the help of a sieve or cloth filter. It may in addition, or as alternative, also be done selectively, leaving a remaining filter fraction or part thereof in the re- actor or the like, or by operating under suitable conditions, such as in a sequence batch reactor, or combinations thereof. Separated residual filter material may be dewatered, such as with a screw press, and taken to a final or further processor.

Mixing this residual filter material with the other sludge is also an option. The effluent from the acidification reactor can also be recycled in its entirety to the WWTP without sepa- ration of fatty acids and residual (unconverted) filter frac- tion.

The pH may be regulated, such as by diluting the filter material with rejection water from the sludge dewatering. This rejection water is found to have a relatively large amount of ammonium and phosphate which provide a buffering effect. In addition, a base may be dosed, such as lime pellets, which may be obtained from drinking water companies.

To prevent sulphate reduction, washing of the filter frac- tion material, whereby sulphate is removed, may be considered as a pre-purification step.

The temperature in the reactor may be variable and may vary with the ambient temperature. Heating the reactor is not a desired option, because it costs too much energy. If resid- ual heat is available, the reactor could be operated at a higher temperature; in that case the residence time may need to be shorter to prevent methane formation.

The combination of fatty acid production, from filter fraction material from the influent, from active sludge, from water treatment itself, or fine filter fraction material from another purification, and optimization of the P and N removal is considered unique. This is an improvement over existing state of the art purification processes for biological P- and N-removal. In this way organic matter in waste water (espe- cially that part that comes from toilet paper) is used to a higher extent in the water purification process. As a result, fewer additives are required to achieve the required effluent quality.

The present method provides for a conversion to fatty ac- ids of 30-60% (based on carbon conversion/available carbon), typically 35-45% conversion. In an example the level of P in the effluent could be lowered to 0.5-2 mgP/l by addition of fatty acids.

Also the denitrification is accelerated, typically 10-20% accelerated (measured in time/time), thereby increasing a ca- pacity of a WWTP.

As mentioned, use of iron (III) chloride is reduced or even no longer required (which may be as much as 300 ton/y/plant). A sludge production is slightly decreased (some 3%), the amount of remaining filter fraction is reduced by 40-50%, and as a consequence about 80 tons of carbon dioxide are not emit- ted into the atmosphere. Further expensive investments in a sand filter can be prevented, at the cost of a five times cheaper fatty acid reactor. It is therefore considered that a return on investment is about 7 years.

Thereby the present invention provides a solution to one or more of the above-mentioned problems.

Advantages of the present invention are detailed through- out the description.

5 DETAILED DESCRIPTION OF THE INVENTION The present invention relates in a first aspect to a method according to claim 1.

In an exemplary embodiment of the present method the filter fraction may be obtained from a water treatment in- stallation, from bacterial sludge, from a process installa- tion, from a cleaning process, from a purification process, and combinations thereof.

In an exemplary embodiment of the present method the filter fraction may be obtained by filtering over a cloth, a sieve, over a filter, in a drum, by centrifugation, and combinations there-of.

In an exemplary embodiment of the present method a par- ticle size of the filtered biological material may be smaller than 3 mm, preferably smaller than 2 mm, more pref- erably smaller than 1 mm, such as smaller than 0.5 mm, e.g. from 0.02-0.4 mm, such as 0.04-0.1 mm.

In an exemplary embodiment of the present method during acidifying the pH may be maintained between 4 and 7, pref- erably be-tween 4.5-6.5, such as at 5.5-6.0.

In an exemplary embodiment of the present method a pH may be maintained by addition of rejection water from sludge dewatering, by addition of a base, such as a calcium comprising base, such as CaCO: comprising base, and combina- tions thereof.

In an exemplary embodiment of the present method a res- idence time during acidifying may be < 20 days, preferably < 10 days, more preferably between 2-6 days, preferably wherein a residence time may be adapted to boundary condi- tions, such as temperature.

In an exemplary embodiment of the present method a fatty acid concentration may be maintained < 40 g/l, pref- erably <20 g/1, such as <10 g/l, such as 0.1-7 g/1].

In an exemplary embodiment of the present method nutri- ents may be added, wherein nutrients are selected from N-

comprising compounds, P-comprising compounds, and micronu- trients. In an exemplary embodiment of the present method a level of N-comprising nutrients may be maintained above 0.1 mg N/1, preferably above 0.2 mg N/1, more preferably above 1 mg N/1, such as above 2 mg N/1, and/or a level of N-com- prising nutrients may be maintained below 100 mg N/1, pref- erably below 50 mg N/l, more preferably below 30 mg N/1, such as below 20 mg N/1.

In an exemplary embodiment of the present method a level of P-comprising nutrients may be maintained above 0.1 mg P/1, preferably above 0.2 mg P/l, more preferably above 1 mg P/1l, such as above 2 mg P/1, and/or a level of P-com- prising nutrients may be maintained below 100 mg P/l, pref- erably below 50 mg P/1, more preferably below 30 mg P/1, such as below 20 mg P/1.

It has been found that these relatively low amounts of N and P, respectively, optionally in combination with deni- trifying elements such as filters, typically provided in a later stage of the process, allow for good fatty acid pro- duction. In addition, maintain amounts of N and P below certain levels provides good control. A minimum concentra- tion may be used to ensure that the biomass continues to grow well, A maximum concentration may be used ensure that a subsequent purification step with VFA does not cause any quality problems with regard to the effluent. Two situa- tions may be considered. A situation where the fatty acid- containing solution is added at the beginning or middle of the purification process. In this case, the ammonium and phosphate concentrations do not matter much and could best be kept both at a minimum of 1.0 mg/l. In a situation where the fatty acid-containing solution is added at the end of the purification process, such as, to sand filters or the denitrification period of a Nereda® process. For ammonium maximum increase may best be limited to 0.1 mg NH4-N/1 by adding the VFA solution; typically this indicates that 1.0 mg NH4-N/1 may be in the VFA solution; for P a maximum in- crease may best be limited to 0.1 mgP/l by adding the VFA solution; typically this indicates that 1.0 mgP/l may be in the VFA solution.

It is noted that when the filter fraction is pre- treated, such as by washing, or in general, it may contain a too limited amount of nutrients, which amount may vary over time, in view of filter fraction source, etc. In such cases nutrients may be added in order to improve conversion to fatty acids.

In an exemplary embodiment of the present method before acidifying the filter fraction may be washed.

In an exemplary embodiment of the present method a sul- phate concentration of the filter fraction may be reduced, such as by washing.

In an exemplary embodiment of the present method a tem- perature during acidifying is maintained at 0-40 °C, pre- fer-ably at ambient temperature.

In an exemplary embodiment of the present method a re- maining filter fraction may be further processed, prefera- bly after de-watering thereof.

In an exemplary embodiment the present method may be for improving removal of P and/or N in a water treatment installation.

In an exemplary embodiment of the present method the method may be operated in a sequence batch reactor, in a continuous batch reactor, in a stirred reactor, in a seg- mented reactor, and combinations thereof.

In an exemplary embodiment of the present method before acidifying the filter fraction may be dewatered, such as to 20-50% dry solid contents, preferably 30-40%.

In an exemplary embodiment of the present method an oxi- dation reduction potential (ORP) is maintained in a range of - 400mV<ORP<-100 mV, preferably between -300mV<ORP<-150 mV, such as -250mV<ORP<-180 mV, such as by increasing or decreasing aeration.

In an exemplary embodiment of the present method the system may be loaded with > 0.5 kg COD, preferably > 1, more preferably >2, per m° system volume/day.

In an exemplary embodiment of the present method the wastewater may be pre-treated, preferably by at least one of clarification, grit removal, fat removal, grease re- moval, pH-adjustment, and pre-sedimentation.

In an exemplary embodiment the present method may fur- ther comprise providing a fatty acid producing system 100 comprising an aqueous filter fraction input 1 and a second in- put 2 for providing an aqueous fluid in fluid connection with sald first input, a reactor 5 and a diluted filter fraction fluid connection 3 from said first input to said reactor, a base reservoir 6 in fluid connection 7 with the reactor for increasing the pH of the fluid in the reactor, a reactor out- put 8 in fluid connection with a filter 4, a filter output 9 for removing fatty acids, a fluid connection 10 between filter and reactor for returning a part of the filter fraction to the reactor, and a surplus filter fraction output 11 for removing filter fraction.

Typically a diluted fluid with 0.5-10 wt. dry solids is provided to the reactor, such as 1-3 wt.% dry solids.

The reactor may comprise controls, such as controls for pH, ORP, N-level, P-level, temperature, solid fraction, fluid level, valves, etc, and combination thereof.

By return- ing a fraction of the processed filter fraction, such as 1-500 times, e.g. 2-50 times, an effective solid retention time is increased significantly.

Typically 1-30 gr/l fatty acids are removed, such as 2-10 gr/l.

In an exemplary embodiment the present method may fur- ther comprise providing a waste water input (21) in fluid connection with a waste water treatment reactor (200), wherein the waste water treatment reactor comprises an outlet (22), the outlet being in fluid connection with a (secondary) set- tler (211), the filter being in fluid connection with an ef- fluent outlet (23) and with a return path (3), the return path being in fluid connection (24) with the inlet of the waste wa- ter treatment reactor and with the a diluted filter fraction fluid connection (3) of the fatty acid producing system (100), the filter output (9) being in fluid connection with the waste water input (21), and the surplus filter fraction output (11) being in fluid connection with the filter output (25) The re- actor and fatty acid producing system may be considered a second aspect of the present invention.

The invention is further detailed by the accompanying figures and example, which are exemplary and explanatory of nature and are not limiting the scope of the invention.

SUMMARAY OF THE FIGURES Figure 1-2 show reactor set-ups. Figure 3 shows cumulative COD conversion to sCOD in column filled with dry (35% TS) SF. Figure 4 shows denitrification test with acidified SF and acetic acid as a reference.

DETAILED DESCRIPTION OF THE FIGURES Figure 1 shows a fatty acid producing system 100 compris- ing an aqueous filter fraction input 1 and a second input 2 for providing an aqueous fluid in fluid connection with said first input, a reactor 5 and a diluted filter fraction fluid connection 3 from said first input to said reactor, a base reservoir 6 in fluid connection 7 with the reactor for in- creasing the pH of the fluid in the reactor, a reactor output 8 in fluid connection with a filter 4, a filter output 9 for removing fatty acids, a fluid connection 10 between filter and reactor for returning a part of the filter fraction to the re- actor, and a surplus filter fraction output 11 for removing filter fraction. Figure 2 shows a waste water input 21 in fluid connection with a waste water treatment reactor 200, wherein the waste water treatment reactor comprises an outlet 22, the outlet be- ing in fluid connection with a settler 211, the settler being in fluid connection with an effluent outlet 23 and with a re- turn path 3, the return path being in fluid connection 24 with the inlet of the waste water treatment reactor and over filter 4 for producing a fine filter fraction with the a diluted fil- ter fraction fluid connection 3 of the fatty acid producing system 100, the filter output 9 being in fluid connection with the waste water input 21, and the surplus filter fraction out- put 11 being in fluid connection with the filter output 25 The figures are further detailed in the description and example below. EXAMPLES/EXPERIMENTS The below relates to an example of the present invention.

Experiments VFA production from Sieve Fraction (SF) of wastewater

1. Percolation of dry sieve fraction A column filled with 1 litre of dry SF (35% TS) was con- tinuously percolated with tap water. Ammonium and phosphate buffer were added to the tap water to prevent nutrient and pH limitation. Temperature in the column was maintained at 37 °C by indirect heating with warm tap water. Soluble COD (sCOD) and VFA’ s were measured in the percolate. In a period of 27 days 25% of the COD in SF was converted to soluble COD, see figure 3. Analysis of the sCOD with HPLC revealed that circa 85% of the COD can be attributed to VFA's; 2/3 acetic acid and 1/3 propionic acid. sCOD concentrations in the percolate were typically 100-200 mg/l. Percolation flow was 3-6 l/day.

Due to flotation of the SF in the column the experiment had to be terminated. Shaking experiments with the rest SF re- maining in the column showed additional conversion of 15% to sCOD. Overall conversion of COD to sCOD was therefore > 40%.

2. Operation of CSTR with pH control Semi continuous operation of a CSTR at 37 °C and pH 6,5. The CSTR was manually fed with wet SF (3% TS) 3-4 times per week. The average HRT was 6 days. sCOD concentrations were circa 8-10 g/l, circa 26% of the COD in SF was converted to VFA’ s.

3. Activated sludge modelling of the effect of feeding ex- tra VFA's to wwtp.

The effect of feeding the produced VFA’s to a wwtp to en- hance biological phosphorus removal was studied with the acti- vated sludge model (ASM3-bioP} in SIMBA. Feeding extra 25% (22,5 mg/l) and 502% (45 mg/l) extra VFA's to the anaerobic tank resulted in a drop of effluent PO4-P from 0,96 mg/l to 0,43 and 0,26 mg/l PO4-P respectively.

4. Denitrification test with sCOD from acidified SF Acidified SF from the CSTR experiment was centrifuged and used as a carbon source in a denitrification batch experiment. The denitrification rate was compared to acetic acid as a ref- erence, see fig 4. Average denitrification rates at room tem- perature (20 °C) were 2,6 and 3,0 g NO3-N/kg DS.hr for acidi- fied SF and acetic acid respectively. Note that the grey dots present the denitrification rate in activated sludge without addition of external carbon source which is representative for most activated sludge installations.

The following section is aimed at supporting the search, of which the subsequent section is considered to be a transla- tion into Dutch.

1. Method of producing fatty acids, comprising obtaining a filter fraction from an aqueous solution com- prising biological material, the dry filter fraction com- prising >50 wt.% organic material, preferably > 80 wt.%, such as > 90 wt.5%, acidifying the filter fraction under anaerobic conditions by microorganisms, by producing fatty acids, wherein the wt.% is based on the dry solids content.

2. Method according to embodiment 1, wherein the filter frac- tion is obtained from a water treatment installation, from bacterial sludge, from a process installation, from a cleaning process, from a purification process, and combi- nations thereof.

3. Method according to any of embodiments 1-2, wherein the filter fraction is obtained by filtering over a cloth, over a sieve, over a filter, in a drum, by centrifugation, and combinations there-of, wherein preferably a particle size of the filtered biological material is smaller than 3 mm, preferably smaller than 1 mm.

4. Method according to any of embodiments 1-3, wherein during acidifying the pH is maintained between 4 and 7, prefera- bly be-tween 4.5-6.5, such as at 5.5-6.0.

5. Method according to embodiment 4, wherein a pH is main- tained by addition of rejection water from sludge dewater- ing, by addition of a base, such as a calcium comprising base, such as Ca-CO03 comprising base, and combinations thereof.

6. Method according to any of embodiments 1-5, wherein a res- idence time during acidifying is < 20 days, preferably < 10 days, more preferably between 2-6 days, preferably wherein a residence time is adapted to boundary condi- tions, such as temperature.

7. Method according to any of embodiments 1-6, wherein a fatty acid concentration is maintained < 40 g/l, prefera- bly <20 g/l, such as <10 9/1.

8. Method according to any of embodiments 1-7, wherein nutri- ents are added, wherein nutrients are selected from N-com- prising compounds, P-comprising compounds, and micronutri- ents.

9. Method according to embodiment 8, wherein a level of N- comprising nutrients is maintained above 0.1 mg/l, and/or wherein a level of N-comprising nutrients is maintained below 100 mg N/1, and/or wherein a level of P-comprising nutrients is maintained above 0.1 mg/l, and/or a level of P-comprising nutrients may be maintained below 100 mg P/1.

10. Method according to any of embodiments 1-9, wherein before acidifying the filter fraction is washed, and/or wherein a sulphate concentration of the filter fraction is reduced.

11. Method according to any of embodiments 1-10, wherein a temperature during acidifying is maintained at 0-40 °C, preferably at ambient temperature.

12. Method according to any of embodiments 1-11, wherein a re- maining filter fraction is further processed, preferably after de-watering thereof.

13. Method according to any of embodiments 1-12, for improving removal of P and/or N in a water treatment installation.

14. Method according to any of embodiments 1-13, wherein the method is operated in a sequence batch reactor, in a con- tinuous batch reactor, in a stirred reactor, in a seg- mented reactor, and combinations thereof.

15. Method according to any of embodiments 1-14, wherein be- fore acidifying the filter fraction is dewatered, such as to 20-50% dry solid contents, preferably 30-40%.

16. Method according to any of embodiments 1-15, wherein an oxidation reduction potential (ORP) is maintained in a range of -400mV<ORP<-100 mV, such as by increasing or de- creasing aeration.

17. Method according to any of embodiments 1-16, further com- prising providing a fatty acid producing system (100) com- prising an aqueous filter fraction input (1) and a second input (2) for providing an aqueous fluid in fluid connec- tion with said first input, a reactor (5) and a diluted filter fraction fluid connection (3) from said first input to said reactor, a base reservoir (6) in fluid connection (7) with the reactor for increasing the pH of the fluid in the reactor, a reactor output (8) in fluid connection with a filter (4), a filter output (9) for removing fatty ac- ids, a fluid connection (10) between filter and reactor for returning a part of the filter fraction to the reac- tor, and a surplus filter fraction output (11) for remov- ing filter fraction.

18. Method according to any of embodiments 1-17, further com- prising a waste water input (21) in fluid connection with a waste water treatment reactor (200), wherein the waste water treatment reactor comprises an outlet (22), the out- let being in fluid connection with a settler (211), the filter being in fluid connection with an effluent outlet (23) and with a return path (3), the return path being in fluid connection (24) with the inlet of the waste water treatment reactor and via a filter (4) with the a diluted filter fraction fluid connection (3) of the fatty acid producing system (100), the filter output (98) being in fluid connection with the waste water input (21), and the surplus filter fraction output (11) being in fluid con- nection with the filter output (25).

Claims

CONCLUSIESCONCLUSIONS

1. Werkwijze voor het produceren van vetzuren, omvattende het verkrijgen van een filterfractie uit een waterige op- lossing die biologisch materiaal omvat, waarbij de droge fil- terfractie >50 gew.% organisch materiaal omvat, bij voorkeur >80 gew.%, zoals >90 gew.%, het verzuren van de filterfractie onder anaërobe omstan- digheden door micro-organismen, door het produceren van vetzu- ren, waarbij het gew.% gebaseerd is op het gehalte aan droge vaste stoffen.A method for producing fatty acids, comprising obtaining a filter fraction from an aqueous solution comprising biological material, wherein the dry filter fraction comprises> 50 wt.% Organic material, preferably> 80 wt.%, Such as > 90 wt.%, Acidifying the filter fraction under anaerobic conditions by microorganisms, by producing fatty acids, the wt% being based on the dry solids content.

2. Werkwijze volgens conclusie 1, waarbij de filterfrac- tie wordt verkregen uit een waterbehandelingsinstallatie, uit bacterieel slib, uit een procesinstallatie, uit een reini- gingsproces, uit een zuiveringsproces, en combinaties daarvan.A method according to claim 1, wherein the filter fraction is obtained from a water treatment plant, from bacterial sludge, from a process plant, from a cleaning process, from a purification process, and combinations thereof.

3. Werkwijze volgens een der conclusies 1-2, waarbij de filterfractie wordt verkregen door filteren over een doek, over een zeef, over een filter, in een trommel, door centrifu- geren, en combinaties daar, waarbij bij voorkeur een deeltje de grootte van het gefilterde biologische materiaal is kleiner dan 3 mm, bij voorkeur kleiner dan 1 mm.A method according to any one of claims 1-2, wherein the filter fraction is obtained by filtering over a cloth, over a sieve, over a filter, in a drum, by centrifugation, and combinations there, where preferably a particle has the size of the filtered biological material is less than 3 mm, preferably less than 1 mm.

4, Werkwijze volgens een van de conclusies 1-3, waarbij tijdens het aanzuren de pH wordt gehandhaafd tussen 4 en 7, bij voorkeur tussen 4,5-6,5, zoals bij 5,5-6,0.A method according to any one of claims 1-3, wherein during the acidification the pH is maintained between 4 and 7, preferably between 4.5-6.5, such as at 5.5-6.0.

5. Werkwijze volgens conclusie 4, waarbij een pH wordt gehandhaafd door toevoeging van rejectiewater uit slibontwate- ring, door toevoeging van een base, zoals een calcium omvat- tende base, zoals CaCO: omvattende base, en combinaties daar- van.A method according to claim 4, wherein a pH is maintained by adding rejection water from sludge dewatering, by adding a base, such as a calcium-comprising base, such as CaCO: comprising base, and combinations thereof.

6. Werkwijze volgens een der conclusies 1-5, waarbij een verblijftijd gedurende verzuring <20 dagen is, bij voorkeur <10 dagen, liever tussen 2-6 dagen, bij voorkeur waarbij een verblijftijd is aangepast aan randvoorwaarden, zoals als tem- peratuur.A method according to any one of claims 1-5, wherein a residence time during acidification is <20 days, preferably <10 days, more preferably between 2-6 days, preferably wherein a residence time is adapted to boundary conditions, such as temperature.

7. Werkwijze volgens een van de conclusies 1-6, waarbij een vetzuurconcentratie wordt gehandhaafd <40 g/l, bij voor- keur <20 g/l, zoals <10 g/l.A method according to any one of claims 1-6, wherein a fatty acid concentration is maintained <40 g / l, preferably <20 g / l, such as <10 g / l.

8. Werkwijze volgens een van de conclusies 1-7, waarbij voedingsstoffen worden toegevoegd, waarbij voedingsstoffen worden gekozen uit N-omvattende verbindingen, P-omvattende verbindingen, en micronutriënten.A method according to any one of claims 1-7, wherein nutrients are added, wherein nutrients are selected from N-comprising compounds, P-comprising compounds, and micronutrients.

9. Werkwijze volgens conclusie 8, waarbij een gehalte aan N-omvattende voedingsstoffen wordt gehandhaafd boven 0,1 mg/l, en/of waarbij een gehalte aan N-omvattende voedingsstoffen wordt gehandhaafd onder 100 mg N/1, en/of waarbij een gehalte van P-omvattende nutriënten wordt gehandhaafd boven 0,1 mg/l, en/of een gehalte van P-omvattende voedingsstoffen wordt ge- handhaafd onder 100 mg P/l.A method according to claim 8, wherein a content of N-comprising nutrients is maintained above 0.1 mg / l, and / or wherein a content of N-comprising nutrients is maintained below 100 mg N / l, and / or wherein a content of P-comprising nutrients is maintained above 0.1 mg / l, and / or a content of P-comprising nutrients is maintained below 100 mg P / l.

10. Werkwijze volgens een van de conclusies 1-9, waarbij voor het verzuren de filterfractie wordt gewassen, en/of waar- bij een sulfaatconcentratie van de filterfractie wordt ver- laagd.A method according to any one of claims 1 to 9, wherein before acidification the filter fraction is washed, and / or wherein a sulfate concentration of the filter fraction is reduced.

11. Werkwijze volgens een van de conclusies 1-10, waarbij een temperatuur tijdens verzuren wordt gehandhaafd op 0-40 °C, bij voorkeur bij omgevingstemperatuur.A method according to any one of claims 1-10, wherein a temperature during acidification is maintained at 0-40 ° C, preferably at ambient temperature.

12. Werkwijze volgens een der conclusies 1-11, waarbij een resterend filterfractie verder wordt verwerkt, bij voor- keur na het ontwateren daarvan.A method according to any one of claims 1-11, wherein a residual filter fraction is further processed, preferably after its dewatering.

13. Werkwijze volgens een van de conclusies 1-12, voor het verbeteren van de verwijdering van P en/of N in een waterbe- handelingsinstallatie.A method according to any one of claims 1 to 12 for improving the removal of P and / or N in a water treatment plant.

14. Werkwijze volgens een van de conclusies 1-13, waarbij de werkwijze wordt uitgevoerd in een sequentie batchreactor, in een continue batchreactor, in een geroerde reactor, in een gesegmenteerde reactor, en combinaties daarvan.The process of any of claims 1-13, wherein the process is carried out in a sequence batch reactor, in a continuous batch reactor, in a stirred reactor, in a segmented reactor, and combinations thereof.

15. Werkwijze volgens een van de conclusies 1-14, waarbij voor het verzuren de filterfractie wordt ontwaterd, zoals tot 20-50% droge-stofgehalte, bij voorkeur 30-40%.A method according to any one of claims 1-14, wherein before acidification the filter fraction is dewatered, such as up to 20-50% dry matter content, preferably 30-40%.

16. Werkwijze volgens één van de conclusies 1-15, waarbij een oxidatie reductie potentiaal (ORP) wordt gehandhaafd in een bereik van -400 mV<ORP<-100 mV, zoals door het verhogen of verlagen van de beluchting.The method of any of claims 1-15, wherein an oxidation reduction potential (ORP) is maintained in a range of -400 mV <ORP <-100 mV, such as by increasing or decreasing aeration.

17. Werkwijze volgens een van de conclusies 1-16, verder omvattende het verschaffen van een vetzuurproducerend systeem (100) omvattende een waterige filterfractie-invoer (1) en een tweede invoer (2) voor het verschaffen van een waterige vloeistof in fluidumverbinding met de eerste invoer, een reac- tor (5) en een verdunde filterfluidum-fluidumverbinding (3) van de eerste invoer naar de reactor, een basereservoir (6) in een fluidumverbinding (7) met de reactor voor het verhogen van de pH van de vloeistof in de reactor, een reactoruitgang (8) in fluidumverbinding met een filter (4), een filteruitvoer (9) voor het verwijderen van vetzuren, een fluidumverbinding (10) tussen filter en reactor voor het retourneren van een deel van het filter fractie naar de reactor, en een overmaat filter- fractieuitvoer (11) voor het verwijderen van filterfractie.A method according to any of claims 1-16, further comprising providing a fatty acid producing system (100) comprising an aqueous filter fraction input (1) and a second input (2) for providing an aqueous liquid in fluid communication with the first inlet, a reactor (5) and a dilute filter fluid-fluid connection (3) from the first inlet to the reactor, a base tank (6) in a fluid connection (7) with the reactor for increasing the pH of the liquid in the reactor, a reactor outlet (8) in fluid communication with a filter (4), a filter outlet (9) for removing fatty acids, a fluid connection (10) between filter and reactor for returning part of the filter fraction to the reactor, and an excess filter fraction output (11) for removing filter fraction.

18. Werkwijze volgens een van de conclusies 1-17, verder omvattende een afvalwateringang (21) in fluidumverbinding met een afvalwaterbehandelingsreactor (200), waarbij de afvalwa- terbehandelingsreactor een uitlaat (22) omvat, waarbij de uit- laat in fluidumverbinding staat met een bezinker (211), waar- bij het filter in fluidumverbinding staat met een effluentuit- laat {23) en met een terugslagbaan (3), waarbij het retourpad in fluidumverbinding (24) is met de inlaat van de afvalwater- behandelingsreactor en over een filter (4) met de verdunde filterfluidumverbinding (3) van het vetzuurproducerende sys- teem (100), waarbij de filteruitgang (9) in fluidumverbinding staat met de afvalwateringang (21), en de overmaat filter fractieoutput (11) die in fluidumverbinding staat met de fil- teruitgang (25).The method of any one of claims 1 to 17, further comprising a waste water inlet (21) in fluid communication with a waste water treatment reactor (200), the waste water treatment reactor comprising an outlet (22), the outlet being in fluid communication with a waste water treatment reactor (22). settler (211), wherein the filter is in fluid communication with an effluent outlet (23) and with a return path (3), the return path being in fluid communication (24) with the inlet of the wastewater treatment reactor and over a filter (4) with the dilute filter fluid compound (3) of the fatty acid producing system (100), wherein the filter outlet (9) is in fluid communication with the waste water inlet (21), and the excess filter fraction output (11) is in fluid communication with the filter outlet (25).