WO2009015405A1

WO2009015405A1 - Method of treating biosolids

Info

Publication number: WO2009015405A1
Application number: PCT/AU2007/001054
Authority: WO
Inventors: Robert Charles Brookes; Steven Gregory Brown
Original assignee: Gro-Mor Pty Ltd
Priority date: 2007-07-27
Filing date: 2007-07-27
Publication date: 2009-02-05
Also published as: AU2007357069A1

Abstract

A method of treating biosolids including: receiving a feedstock of biosolids for treatment; assessing one or more feedstock characteristics inherent in the feedstock; adding one or more feedstock additives selected to adjust at least one of the feedstock characteristics within a predetermined range to provide a preadjusted feedstock, the one or more feedstock additives including a bioactive component having included therein liquid piggery waste; adding chicken manure in solid or semisolid form to the liquid piggery waste to provide a liquefied chicken manure; initialising bioactivity in the preadjusted feedstock to provide a bioactive mixture; and maintaining the bioactivity in the bioactive mixture for a time sufficient to produce a biotreated product.

Description

"Method of Treating Biosolids"

FIELD OF INVENTION

THIS INVENTION relates to a method of treating biosolids. The invention has particular application to the treatment of biosolids from selected waste sources which have a relatively stable composition within from defined parameters. However, the invention is not limited to this field of use.

In this specification, the term biosolids refers to solid waste material which is formed as a by-product of sewage treatment, including not only sewage in general as may be received into municipal waste treatment facilities, but also waste material from* specific agricultural or biological processes or industries not necessarily fed into and mixed with general sewage.

BACKGROUND ART

The traditional method of treating biosolids typically involves dumping into land fill. Where treatment is undertaken, treatment processes are usually continuous. Waste treatment regimes often involve the collection of waste waters and/or waste carrying waters from a diverse range or sources, mixing them together, and treating the mixed material in a general waste treatment plant. As a result, the biosolids produced by the removal of wastewater can be variable in their content. Complete digestion of the biosolids is rare or sometimes not possible.

The present invention aims to provide a method of treating biosolids which alleviates one or more of the disadvantages of the prior art. Other aims and advantages of the invention may become apparent from the following description.

DISCLOSURE OF THE INVENTION

With the foregoing in view, this invention resides broadly in a method of treating biosolids including:

receiving a feedstock of biosolids for treatment; assessing one or more feedstock characteristics inherent in the feedstock; adding one or more feedstock additives selected to adjust at least one of the feedstock characteristics within a predetermined range to provide a preadjusted feedstock, the one or more feedstock additives including a bioactive component having included therein liquid piggery waste; adding chicken manure in solid or semisolid form to the liquid piggery waste to provide a liquefied chicken manure; initialising bioactivity in the preadjusted feedstock to provide a bioactive mixture; and maintaining the bioactivity in the bioactive mixture for a time sufficient to produce a biotreated product. Preferably, the method includes adjusting the liquidity of the feedstock. In such form, one of the additives is a liquefier which preferably includes other additives for adjusting such characteristics as, for example, pH and/or deficiencies in one or more nutrients required for bioactivy. In a preferred embodiment, all of the additives and the bioactivity initiation are provided in a single liquid additive. Preferably, the liquid additive includes an alkaline additive component, more preferably having free nitrogen therein. It is also preferred that the single liquid additive includes a bioactive component.

For example, liquefied chicken manure may be used as the alkaline additive component since it is likely to be alkaline as well as having free nitrogen contained therein. The bioactive component may, for example, be in the form of liquid piggery effluent since it is likely to be biologically active. The liquid chicken manure may be provided by adding chicken manure in solid or semisolid form to the liquid piggery waste. Alternatively or in addition thereto bioactivity may be provided by inoculation and/or the pH may be adjusted by addition of mineral acid and/or alkali.

It is preferred that the pH of the liquid additive component be in the range of from 8 to 10, more preferably pH 9. In such form, it is preferred that the nitrogen content of the chicken manure be about 6.2%, and be added to the piggery effluent in ratio of about 2'Λ to 1 such that after addition to the feedstock, the mixture has a pH in the range of from 7 to 8. It is preferred that the single liquid additive is added to the biosolids feedstock in the amount of from 10% to 50% by volume. The bioactivity of the mixture after its adjustment typically commences within 24 to 48 hours. The bioactivity is manifested by the production of gas bubbles, typically containing predominately methane and other products of anaerobic digestion. The mixture is typically stirred at intervals ranging from daily to once every several weeks. The bioactivity is substantially completed when the production of gas bubbles ceases or substantially ceases after a period ranging from one to twenty-four months.

In another aspect, the present invention resides broadly in treated biosolid product formed by the method herein described.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate two preferred embodiments and wherein:

Fig. 1 is a plan view of a biosolids treatment plant operable to perform the method of the invention;

Fig. 2 is a cross-section of one of the ponds of the plant of Fig. 1;

Fig. 2 is a plan view of an alternative biosolids treatment plant operable to perform the method of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The biosolids treatment plant 10 has set out thereon the elements required for the performance of the method of the present invention. The area includes a receiving area 11 where feedstock is assessed as to one or more of its inherent characteristics. A series of thirteen ponds shown typically at 12 are provided in spaced side-by-side relationship. Each pond is in the form of an elongate rectangle in plan view, each also of substantially the same length. The feedstock is directed to the ponds after being adjusted in one or more of its characteristics by addition of. additives in accordance with the invention. The ponds are filled one at a time so that each of the thirteen ponds is at a different stage of biodigestion. Each pond has a cross section shown in Fig. 2, the sides of the pond having a sloped portion 13 and a concave base 14. The sloped sides are at approximately 45° or a 1:1 slope whereas the shallow concavity of the base is substantially to a central valley 15 at a fall of approximately 5%. The sides of each pond extend up to respective intermediate zones shown typically at 16. Each zone is almost flat, having a fall of approximately 1% downward in the direction of arrow 17 for safety. A redirection sill 18 surrounds the area of the plant. An access ramp shown typically at 19 slopes upward to a level above the zone near to, but spaced from one of the ends of each pond. Such a feature enables machinery to have elevated access to the pond. Each pond also has a fall along its length of approximately 0.5%.

Typically the width of each pond is between 17.5 and 18 metres with a length of approximately 116 metres. The slope of the access ramp is about one in eight, and the height of each sloped portion 13 is approximately 2.7 to 3 metres. There is a drying area 20 provided along the ends of each of the ponds remote from the receiving area and extending across the width of the land area as determined by the sum of the width of each of the ponds together with their spacing from one another. It can be seen that the ponds are substantially alongside one another in parallel formation with each of their ends substantially aligned. An embankment shown typically at 21 is provided to accommodate contours of land and respective ramp embankments shown typically at 22 arranged to provide the access ramp as shown. Downhill from the drying area there is provided a contaminated run off, recycling and/or evaporation pond 23. Successive contour lines shown typically at 24 are provided to show increasing elevation in the direction of arrow 25. Thus it can be seen that the pond at the bottom of Fig. 21 will be at a slightly lower elevation than the pond at the top of Fig. 1.

The alternative plant 30 shown in Fig. 3is able to perform the method of the invention much the same as that shown in Fig. 1. However, the ponds are replaced by a series of tanks shown typically at 31. The alternative receiving area 32 is provided in the form of a shed or the like, the alternative plant being sited adjacent a sewage treatment plant notionally at the location indicated by reference numeral 33. Feedstock is prepared in a concreted covered area 34 which contains an admixture hopper 35 , a biosolids hopper 36 and a mixing tank 37. The hoppers are in fluid connection to the mixing tank by a feed line 38. A feed main 39 branches from the mixing tank to the top of each of the digestion tanks 31. Anaerobic digestion or fermentation takes place with the assistance of the feedstock additives in accordance with the present invention. The tanks are typically filled one at a time to allow fermentation to be staggered stagewise in each of the eight tanks shown in the tank farm. An outlet main 40 is connected from the base of each of the digestion tanks. The outlet main proceeds to a run down screen 41 and then to a rotary screw press 42 for pressing the biosolids of the method of the invention. Dewatered sludge is then stored in a bunker 43 for distribution to a drying pad 44. A contamination runoff pond is also provided in similar fashion to that described and shown in Fig. 1. A diversion bank 45 is also provided in similar fashion to that shown in Fig. 1. A recycled waste water tank 46 is also provided to receive recycled waste water for reuse or supply externally of the plant as the case may be.

DETAILED DESCRIPTION OF THE EXAMPLES

In order that the invention may be more readily understood and put into practical effect, reference will now be made to one or more examples which illustrate a preferred embodiment of the invention.

EXAMPLE l

A sample feed stock additive was prepared by mixing 25 tonnes of chicken manure with ten tonnes of piggery effluent. The chicken manure had a free nitrogen content of approximately 6.2 per cent and resulted in an additive liquid having a pH approximately 9. A feedstock additive was added to biosolids, the amount of biosolids being such that the additive was 15 per cent of the mixture. The pH was tested and found to be in the range of 7 to 8. Biological activity commenced approximately 15 hours after the mixing of the additive with the biosolids. The mixture was stirred every two to three weeks until the sludge was ready for removal. After about four months, the fermentation had completed as evidenced by the substantial reduction of the production of gas bubbles to almost zero. Excess water was pumped from the pond and the sludge removed and placed on a drying pad. The sludge was dried out to about 50% to 60% moisture to produce a partly dried product. The product was then placed in large windrows. The product was then further dried by spreading out on the drying pad approximately 150 mm thick. The product was then arranged into small windrows approximately 1500 mm high. The drying process took approximately six weeks. The drying of the product was monitored to prevent aerobic processes occurring. In the case of the smaller windrows, the drying product was dried to 15% moisture. The product was then screened across a 5 mm screen, aerating the product to produce an odourless product. The product was found to be useful in agriculture as a fertiliser or soil conditioner. At least some of the product was pelletized for ease of packaging and handling.

In use, the method of the present invention may be used to convert biosolids, typically a waste material requiring fertilised material may be produced by following the method according to the invention. Such material is typically formed by drying a digested effluent as herein described. The biosolids added thereto until the additive concentration is approximately 15 per cent by volume.

By selecting the appropriate media for adjusting the parameters of the feed stock additive, the desired parameters of the mixture incorporating the biosolids with the additive can be achieved. Moreover, if desired, inorganic alkaline material may be added such as caustic soda, or free nitrogen in the form of nitrate and/or ammonia.

Although the invention has been described with reference to specific examples, it will be appreciated by persons skilled in the art that the invention may be embodied in other forms which are encompassed within the broad scope and ambit of the invention as herein set forth.

Claims

1. A method of treating biosolids including: receiving a feedstock of biosolids for treatment; assessing one or more feedstock characteristics inherent in the feedstock; adding one or more feedstock additives selected to adjust at least one of the feedstock characteristics within a predetermined range to provide a preadjusted feedstock, the one or more feedstock additives including a bioactive component having included therein liquid piggery waste; adding chicken manure in solid or semisolid form to the liquid piggery waste to provide a liquefied chicken manure; initialising bioactivity in the preadjusted feedstock to provide a bioactive mixture; and maintaining the bioactivity in the bioactive mixture for a time sufficient to produce a biotreated product.

2. The method according to Claim 1 including adjusting the liquidity of the feedstock.

3. A method according to Claim 2, wherein one of the additives is a liquefier which includes other additives for adjusting characteristics.

4. A method according to Claim 2 or Claim 3, wherein all of the additives and the bioactivity initiation are provided in a single liquid additive.

5. A method according to Claim 4, wherein the liquid additive includes an alkaline additive component.

6. A method according to Claim 5, wherein the alkaline additive component has free nitrogen therein.

7. A method according to any one of claims 4 to 6, wherein the single liquid additive includes a bioactive component.

8. A method according to Claim 7, wherein the single liquid additive component includes liquefied chicken manure.

9. A method according to Claim7 or Claim 8, wherein the bioactive component includes liquid piggery effluent.

10. A method according to any one of the preceding claims, wherein the nitrogen content of the chicken manure is about 6.2%, and added to the piggery effluent in ratio of about 2¹A to 1 such that after addition to the feedstock, the mixture has a pH in the range of from 7 to 8.

11. A method according to any one of Claims 4 to 10, wherein the single liquid additive is added to the biosolids feedstock in the amount of from 10% to 50% by volume.

12. A method according to any one of the preceding claims including stirring the mixture at intervals ranging from daily to once every several weeks.

13. A treated biosolid product formed by a method defined by any one of Claims 1 to 12.