Patent Application
20210221726
This invention relates to the processing of high solids Biosolids Cake into pumpable liquid organic fertilizers, and resulting improved organic fertilizers.
Raw sewage is a mix of water and wastes from domestic, commercial and industrial life that are flushed into the sewer. These wastes include both biologically and inorganically derived solids, semi-solids, semi-liquids and liquids, including water.
Raw sewage is treated to retrieve water that the waste process and sewering put into it. This is often conducted in treatment plants (with 1 or more stages) whereby sewage is digested, and then water is separated and cleaned so that it may be safely treated and discharged as effluent. The solids management side of the overall wastewater treatment process often includes a mechanical or chemical/mechanical de-watering step.
Once the water is removed to one degree or another, the remainder from the process is herein termed ‘sewage sludge’. This sewage sludge is often a dry cake-like material having many of the characteristics of a solid or semi-solid. In this application the word solid applies to materials which do not flow under gravitational forces and ambient temperatures or are essentially not pumpable within routine industrial processing requirements, as herein provided. In this application solid sewage sludge is referred to as “Biosolids Cake” or just “Cake” or by the acronym ‘BSC’.
BSC is the result of de-watering to reduce the volume of digested or undigested raw sewage and thereby reduce the consequent transport complications of dealing with the high volume of and the cost of further processing of sewage waste. Without dewatering such waste originally includes as much as 95-97% water, a 3-5% Biosolids component, and often unwanted and/or other dangerous components.
For the purposes of this patent application, biosolids cake is understood that it could also include some undigested de-watered raw sewage.
The biosolids cake is a sticky solid with little or no slump. biosolids cake has many gel-like characteristics and is only readily transported or used as a solid mass. Even this has challenges as it is and remains sticky and difficult to work with.
This biosolids cake can then be further treated or processed into a useful biosolids material referred to by the USEPA as, “The (biosolids) are nutrient-rich organic materials resulting from the treatment of domestic sewage in a treatment facility. When treated and processed, these residuals can be recycled and applied as fertilizer to improve and maintain productive soils and stimulate plant growth.”
Biosolids cake is a broad spectrum material containing many types and quantities of reactants, each mainly organic in nature. Properties of these materials cannot be expected to be entirely fixed in time or quantity. These materials also cannot be expected to have instant reactions with any process, alkali driven or not.
A batch of biosolids cake is typically fairly homogeneous (coming from processing by centrifuge or filter) with respect to content (including moisture) throughout and is gel-like and generally sticky to handle. Diluting the gel-like material into a more dilute fairly homogeneous mixture, say from 25% biosolids to 15% biosolids, does require mixing and does not require aggressive shearing. It is a bit like a jam to a jelly but still a solid.
In terms of free and bound water and dilution, dilution of 25% centrifuged or filtered BSC is easy because the material has retained its bound water and the material is just diluted by adding in additional free water.
This application relates to the manner of processing of solid de-watered sewage and biosolids cake.
For ease of transporting sewage sludge that has been treated and is ready for disposal, the sludge should be:
These two parameters, i.e. high solids-content and low viscosity, conflict.
Most often raw or waste activated sewage sludge sent to the solids management side of the wastewater treatment plant has a solids-content of around three percent, by weight. Flocculation processes usually assist and are common. Thus, in a tonne of this material, 30 kg is solids, and 970 kg is water. At the sewage treatment plant, the raw 3%-sewage is de-watered. Simple de-watering (in which the water is basically squeezed out of the sludge, mechanically, is effective to remove a great deal of the water content of the sludge (i.e is effective to increase the solids content). Simple thickening can be effective to increase the solids content to around 10 or 15%. Centrifuging can be effective to further increase the solids content to i.e. 20%, or even higher. The upper limit of (economical) mechanical de-watering of this type of organic sludge may be considered to be about 25%-solids.
After de-watering to 10% solids, the 30 kg of solids in the initial tonne of raw 3%-sewage, now is accompanied by only 270 kg of water (the other 700 kg of water having been squeezed out). After de-watering to 25% solids, the 30 kg of solids now is accompanied by only 90 kg of water (i.e at 25%-solids, 880 kg or 91% of the water content of the raw 3%-sludge has been squeezed out). Untreated sewage sludge that has been de-watered to 15% solids or more, typically, is stiff, dry and cake-like.
Untreated biosolids 15%-cake and above (Biosolids Content 15%+), unprocessed, is quite unpumpable in the usual liquid handling pumps and a measurement of its viscosity is largely meaningless.
For easy pumpability at ambient temperatures sewage sludge should have a viscosity of 6,000 centiPoise (cP) or less. However, sludge close to 10,000 cP is still just about pumpable (i.e. at increased pumping pressures), but 10,000 cP should be regarded as a reasonable upper limit of viscosity for pumpability. Above that, the sludge requires more expensive mechanical systems and types of pumps. In more detail: for present purposes, sludge at 6,000 cP or less is easily pumpable; sludge between 6,000 and 8,000 cP is pumpable, but not so easily or economically; sludge between 8,000 and 10,000 cP is pumpable, but only with difficulty and increased cost; and sludge above 10,000 cP requires differing types of pumps and larger motors. The viscosity values referred to in this application, measured in the laboratory at room temperature, or at 20-24 C, take into account the preferred end application of the biosolids product as a liquid fertilizer. The viscosity of the biosolids liquid product must take into account the potential for pumping through standard agricultural liquid fertilizer application equipment.
One method of dealing with waste biosolids cake is simply to transport its now lower volume to landfill.
Another alternative is to dry (as by thermal drying) the biosolids cake to a rigid and dry solid pellet form at around 90% biosolids (or more) and treat the pellet sized hard materials as an organic granular fertilizer. Unfortunately, this pellet method is expensive and results in a more expensive fertilizer product from which organic, non-organic and/or dangerous contaminants have not been well removed, with few options.
There are traditional treatment technologies for lowering the viscosity of de-watered sewage sludge and Cake. Lower viscosity is an industrial process objective which assists in reasonable pumpability which in turn affects all aspects of industrial processing of sewage.
Another conventional approach is to raise the temperature to about 160-180 C in a pressure reactor over a period of time of reaction.
Other methods involve additionally raising the pH of the sludge at various temperatures. For instance, alkali, when added to sludge during thermal treatment, raises the pH of the sludge and promotes hydrolysis reactions that break down biological materials in the sludge. It is understood generally that the higher the temperature and pH of the sludge during thermal treatment, the greater the disruption of the sewage sludge and the greater the rate of disruption of that sludge.
Thus, in perhaps over-simplified terms, it is generally understood that the lowest viscosity is procured over time when the sludge is raised to the highest temperature and the highest pH.
It is also understood that there is a diminishing-returns effect, in that, when the temperature and pH have been raised to high levels, the viscosity-lowering effect of a further incremental raise is smaller than the viscosity-lowering effect of the same incremental raise at the lower levels.
Another method is to process relatively dry de-watered Cake having a biosolids content of about 15% or less at atmospheric pressure by a combination of an increased temperature less than 100 degrees Celsius, plus raising the pH, accompanied by violent mechanical shearing.
In many cases, as mechanical/chemical de-watering can readily produce biosolids cake with a higher biosolids content, process water is added to a de-watered Cake with a higher level of biosolids. This is considered a workable but necessary action which, along with the other steps, are required to process the Cake into a pumpable material.
Although effective for purpose, this process is not known for effectively processing high solids Cake of 18-24+% biosolids into a pumpable liquid without adding water to the input material so as to reduce its solids content to less than 15%. This counter-productive step of adding water after transport to process input material, after that material was originally de-watered to a high level before transport, adds cost and complexity which could not, in the prior art, be effectively overcome in an economical industrial process.
A fourth and expensive treatment of incineration is not a good recycling environmental practice.
In one of the present inventor's prior applications the characteristic of pumpability was achieved at previously unknown biosolids contents by an additional step of aggressive shearing. Such shearing attacked the biological materials in the Biosolids Cake and changed their properties to admit of a relatively homogeneous pumpable liquid at 15-18% Biosolids content.
Another method of dealing with waste Biosolids Cake is simply to transport its now lower volume to landfill.
It is generally understood that High Solids Cake (HSBC) and very high Biosolids Cake (VHBSC) beyond that to a lesser extent XHBSC-Cake, (extremely high biosolids content Cake with a solids content of 25% to about 30% or more) despite being de-watered as described above, still contain a measure of loosely bound up (or free water) while remaining in a solid condition. A rule of thumb is that the higher biosolids content cakes appear and act dryer as increased-solidity solid materials. At the extreme, at 90% or more biosolids the XHBSC-Cake is a hard material which must be ground or broken up into a sufficiently pourable dry mass of independent particles for use. An in-use example is pelletized biosolids fertilizer. This is a granular material which is broadcast over the land of application, typically golf courses.
In most cases, solid Cake of 15% to 30% may be further mechanically or chemically de-watered by, for instance, increased and substantially increased mechanical pressure as in a filter or by increased centrifugation. These increased pressures are, however, expensive to obtain and maintain in an industrial process and previously not known to be economically useful beyond drying up an already dryish and solid material to a higher level of the same material.
For industrial purposes the term “Free Water” sets out a useful if somewhat loose criterion for that part of the water content of Cake which may be economically and reasonably extracted by mechanical means. Necessarily, decreasing the level of Free Water in any Cake becomes more and more uneconomic. In many cases, decreasing Free Water in Cakes of 15% biosolids becomes increasingly more expensive as the biosolids content of the material rises from 15% to 24% and even more from 24% through 25%, 26% to 30% and beyond.
By way of description, 15% Biosolids Cake contains a lot more Free Water content than does 30% Biosolids Cake. Above 30% the amount of Free Water becomes increasingly difficult to obtain or measure and by 90% the Biosolids Cake contains no Free Water. The present applicant finds that a reasonable commercial measure of the Free Water limit arises in an about the level of 24%-25% biosolids.
Disposal and/or subsequent use of Biosolids Cake remains a serious and costly problem in the field of sewage disposal.
Transportation of the Biosolids Cake is only part of the issue due to high volumes and costly processes.
Efforts continue to efficiently deal both with raw sewage and with the Biosolids Cake waste product and in doing so recover some or all of any commercial utility remaining in the water and the Biosolids Cake components, whether as solid biosolids components or derived liquids. Recovery and ease of commercial utility remain elusive as the processes involved are uncertain, variable and costly to implement on an industrial scale. They also require significant control, measurement and monitoring due to the variability of the sewage materials themselves.
An added complication arises from the all-to-common entrainment of harmful biologicals and inorganics within the waste.
Levels of possible biological and chemical contaminants in biosolids fertilizers are regulated by national and/or regional agencies and wastewater quality entering municipal wastewater plants is also regulated.
In this application the following are defined terms:
Solid in respect of sewage waste indicates a material which is firm and stable in shape, not a liquid or a fluid. A solid as defined herein does not slump appreciably under gravity alone during process-relevant periods of time at ambient or room temperature and atmospheric pressure.
Fluid in respect of sewage waste indicates a material which has no fixed shape and yields easily to external pressure; a liquid or a slurry. As such a slurry as defined herein slumps appreciably under gravity alone in process-relevant periods of time at ambient or room temperature and atmospheric pressure.
Weight/weight (w/w) expressed in %, is the weight of the Biosolids Components in a BSC sample over the total weight of the sample.
Bio-Solids Cake (BSC) is a solid sewage waste bulk material requiring more expensive pumping and/or conveyance systems by commercial waste disposal methods at ambient or room temperature and atmospheric pressure which is the result of processing raw sewage waste through digesters and De-Watering Processes. Typically, Biosolids Cake at ambient temperature—atmospheric pressure is sticky and somewhat gel-like in some of its characteristics. Biosolids Cake contains at least 15-30% Bio-Solids Components (BS). Typical commercial de-watering of sewage waste produces Biosolids Cake in the range of 20-25% biosolids components. For the purposes of this patent application, Biosolids Cake is understood to also include undigested dewatered raw sewage.
Pumpable applies to Bio-Solids sewage waste material in slurry, suspension, fluid or liquid form which has a viscosity of less than 6,000 cP (centi-poise) at ambient temperature and atmospheric pressure.
Pumping includes pressure driven transfer of Biosolids waste material in slurry, suspension, fluid or liquid form. Pumping includes gravitational and fluid pressure flow as a mass.
De-watering Processes (DWP) are commercial processes which reduce the water content of processed sewage waste by mechanical means commonly at ambient temperature or less than 100 degrees Celsius such as filtration, centrifugation and flocculation. DWP are principally directed at removal of Free Water.
Free Water is that watery component of processed sewage sludge which is not tightly bound to the Bio-Solids Component of the Biosolids Cake. Free Water can readily be squeezed out of (removed from) raw sewage or Biosolids Cake.
Bio-Solids (BS) are the organic components of sewage waste which may be extracted from sewage waste in a solid form.
Drying and Dried as used herein are the removal of water from Biosolids Cake principally directed at removal of tightly bound water from the Bio-Solids Component of Biosolids Cake such as by evaporation and/or desiccation. Drying may be partial or complete, with a full range in between. Drying and de-watering may overlap due to;
Drying as used herein changes the characteristics of the BS Components.
For instance, in the case of complete drying, bio-solids fertilizer pellets are often manufactured by first applying De-Watering Processes to Biosolids Cake up to a commercially expedient level, and, second, the end product DWBSC (de-watered Biosolids Cake) is dried, as by heating and/or thermal evaporation, through to a hard pellet form. This hard pellet form is typically applied to golf courses and the like by mechanical scattering in the manner of granular inorganic fertilizer.
Bio-Solids Component is that part of Biosolids Cake including only organic materials and excluding the water.
Evaluating includes both concurrent and non-concurrent measurement of or use of viscosity parameters, including plant operation in accordance with previously established viscosity parameters proven successful.
Viscosity as used herein is a measure of the resistance to gradual deformation of a fluid by shear or tensile stress at room ambient temperature and atmospheric pressure as measured in centiPoise (cP).
Mixing and mixing/shearing as used herein apply to application of mixing with the objective of simple mixing in of process water to facilitate the hydration step, i.e. the intimate mixing together of water and the dried or partially dried BioSolids Component in the Cake. This mixing breaks up dried (macroscopic) lumps of material producing a fairly homogeneous liquid or slurry without the destruction of the organics themselves. Mixing/shearing as used herein is different from the shearing/aggressive shearing as described in my prior art patents as shearing/aggressive shearing has the objective of disintegrating/tearing apart organics and cellular structures. Shearing/aggressive shearing is a much much more energy intensive process than mixing/shearing.
It is a object to provide stable processes for further commercial processing of high biosolids (HSBSC) content Biosolids Cake derived in bulk from sewage waste into viable improved high biosolids content biologically and environmentally appropriate fertilizing products, as pumpable liquids.
It is a further object to provide for further processing of Biosolids Cake which may be applied across a wide variety of input high biosolids content Biosolids Cake (HSBSC) conditions and compositions.
It is a still further object to render solid Biosolids Cake bulk input material into a verifiable high biosolids content pumpable liquid fertilizer.
It is yet a further object to provide a high biosolids content pumpable liquid which is stable or may be rendered stable by further commercially expedient environmentally appropriate processes.
It is a still further object to provide commercial processes whereby bulk Biosolids Cake may be rendered into high biosolids content pumpable liquid and separable down stream components.
It is an object of the invention to provide for further processing of high biosolids content Biosolids Cake into a high biosolids content pumpable liquid across a wide variety of input BSC compositions, wherein biosolids components comprise 15%-25% or to 30%, or higher, of the composition of the input biosolids Cake without regard to the actual free water components of the input material beyond the results of commercially expedient DWP.
It is an object of the invention to change the properties of the Biosolids Component of Biosolids Cake to achieve at least pumpability at high biosolids concentrations.
It is an object of the invention to achieve high biosolids concentrations in liquids such as slurries wherein the properties of the biosolids components themselves have been altered.
It is yet a further object to render very dry and hard (around 90% Biosolids or more) Biosolids Cake materials into processable biosolids material by mechanical break up of the solid, as by grinding, milling, chopping, etc. to permit effective processing of high biosolids cake with altered properties. This mechanical breaking up provides for particle size reduction.
It is yet a further object of the invention to achieve improvements in the downstream processing capabilities of Biosolids Cake by altering its properties rather than by use of dilution by increasing the Free Water content.
It is a still further object of the invention to provide highly concentrated liquid bio-solids organic fertilizers ready for application by injection and direct absorption into the soil.
An aim of the present technology is to provide a new and more cost-effective way of treating high-bio-solids solid sewage sludge Cakes (HSBSC), particularly:
It is a further objective to obtain a large increase in the extent to which the viscosity of BS Cake, and particularly HSBSC, VHBSC-cake and XHBSC-Cake, can be lowered to economically pumpable ranges, and kept in such ranges, without the use of mechanical severe shearing or complex pressure vessel technology.
A yet further objective is to more efficiently harness reactions to create a greater and more vigorous degree of disruption hydrolysis in complex biological materials and the cellular and other structures within the Cake, and particularly, HSBSC, VHBSC Et XHBSC-Cake than has been done traditionally.
The invention provides a process and procedure whereby pumpability of an environmentally appropriate organic fertilizer product may be obtained or increased starting from a solid Biosolids Cake by adding water back in to the solid Biosolids Cake material which has first had varying amounts of bound water (not free water) removed by drying the biosolids component. The water addition includes mixing such as to break down particulate matter produced as a result of the partial or more fully drying process to produce a fairly homogeneous suspension.
More aggressive mixing after adding back water is an option where further reduction in particle size is required.
Wet or dry milling prior to adding back water are other options.
The objective is to reduce particle sizes of particles and lumps produced through the drying step as a process control to achieve a fluid/slurry which can be evaluated and used as a pumpable liquid fertilizer.
The present invention provides a procedure and a product wherein Biosolids Cake, and particularly the Bio-Solids Component of a solid Biosolids Cake, in solid form in bulk, is first exposed to a drying condition at atmospheric pressure, and, then, second re-hydrated by mixing in water, and, third evaluated as to pumpability preferably less than 6,000 cP.
The present invention provides an industrial procedure wherein the drying condition removes water not otherwise considered to be Free Water, preferably at 24-25% bio-solids and beyond. The drying of the invention irreversibly affects the characteristics of the the biosolids component of the solid Biosolids Cake.
At low biosolids content, while still having solid characteristics, i.e. below 24%, the drying of the invention is principally directed at the biosolids component of the solid Biosolids Cake. Particularly, drying at the surface of the solid Biosolids Cakes is preferred over drying generally as volume drying, such as by drying while stirring, will direct the drying towards the Free Water content more than the biosolids component and tend to produce more of an undesirable generally reversible process.
Above 80-85% biosolids content the DBSC (dried Biosolids Cake) no longer exhibits the sticky characteristic which normally inhibits or prevents grinding or pounding the DBSC into a pourable powder of independent particles. As dryness is increased towards this 80-85% limit the level of required stirring or mixing increases. Above this limit grinding or the like is required to produce a pourable powder of independent particles either before re-hydration or as grinding in the presence of water to achieve the same result.
By this process, Biosolids Cake, VHBSC-cake and XHBSC-Cake, are efficiently rendered pumpable over the required reaction period at atmospheric pressure.
The invention provides an industrial procedure wherein:
The invention also provides an industrial procedure and product for improving pumpability of a mass of solid high solids biosolids cake wherein the procedure does not include aggressive shearing of the mass.
The invention provides an industrial procedure and resulting product for improving pumpability of a mass of solid high solids biosolids cake wherein the biosolids content of the mass is increased to one of 24-25% w/w for 25-30% in the first step and the re-hydration step produces a re-hydrated mass with a biosolids component content of either 18% w/w or 25% or more.
Further the invention provides an industrial procedure for improving pumpability of a mass of solid high solids biosolids cake where in the biosolids component content of the mass is more than 80% in non-sticky hard pellet form after the first step, including a step of grinding the pellets, along with mixing and evaluating.
Further the invention provides an industrial procedure and resulting product for improving pumpability of a mass of solid high solids biosolids cake wherein either the re-hydration step includes the addition of a hydrolizing agent, (preferably lime) and/or an extended period of further thermal incubation following completion of the mixing step.
Further the invention provides an industrial procedure and resulting product for improving pumpability of a mass of solid HSBSC, including a biosolids component of greater than 10% w/w and limited free water, as an organic liquid fertilizer, comprising;
The invention also provides a procedure and product wherein the procedure is carried out at ambient atmospheric pressure.
Title: Table 1 Summary from Individual Thermal Treatment (Drying) (Except Microwave) without Lime
Title: Thermal Treatment (Drying) Experiments (Except Microwave) without Lime
Estimated Solids content of Liquid Product at 6000 cP (Next Day Values)
Title: Table 2 Microwave Thermal Treatment (Drying) without Lime
Title: TABLE 2a Microwave Thermal Treatment (Drying) without Lime
Title: Table 3 Thermal Treatment (Conventional Drying Except Microwaved) with Lime Addition
Title: Table 4 Microwave Thermal Treatment (Drying Experiments with Lime Addition)
Title: Microwave Thermal Treatment (Drying) Experiments with Lime
Title: Table 5: Non-Thermal Air Drying (Low Temperature) without and with Lime
Solids Content of Liquid Product at 6000 cP (Next Day Values)
Title: Table 6. Drying without Heat ie Dehumidification Drying Followed by Aggressive Mixing
Title: Table 7. Dehumidification Drying with Convention Oven Completion
Title: Table 8. Rehydration 90% Air Dried Biosolids (Quick Mix) to 45% Pumpable Liquid: Effect of Lime Concentration
Title: Table 11 Summary of Options: Drying to Produce High Concentration Pumpable Liquids or Slurries
Some examples of preferred procedures that embody the present technology will now be described.
The present Bio-Solids Cake treatment procedure can be controlled by monitoring/evaluating the pumpability of results until a required degree of pumpability has been achieved and then periodically re-hydrating and evaluating for a preferred degree of pumpability over a period of time.
The first 5 rows of Table 1,
The first preferred embodiment shown in
Further, this first embodiment may include additional repetitive extra steps each being:
Details of the operation of the first embodiment are shown in
In these prior art cases a mass of 24% Cake, col 4, was subjected to prolonged heating at 121 and 95 degrees Celsius (col 2) for 1.5 and 18 hours (col 3) respectively. In each case the resultant 24% (non-evaporated) Cake was diluted with water to 18 and 15% solids as noted in column 6 by mixing, col 7, and the viscosity evaluated as shown in col 8. As shown in this prior art, mixing water into the autoclaved and diluted at 18,069 cP Cake at 18%, by shaking, as in row A, produced an unpumpable material, col 8. Adding an aggressive mixing component, referred to and known as shearing/aggressive shearing (such as provided in a household blender for small batches), to the mixing reduced the 18% mix to pumpable at 3,743 cP. Shearing was accomplished by a Ninja Single Serve™ blender. By the next day the viscosity of this batch (ambient temperature) had increased on its own to 4,853 cP irreversibly.
The water bath prior art examples shown in rows B and C (95 degrees Celsius) for 18 hours (col 2 and 3) were diluted to 15% solids and sheared to reach a viscosity of about 4,000 cP.
As shown in row F, a first preferred embodiment, a 25.6% solid Cake material when heated to 97 C for 18 and 24 hours, with evaporation, reached biosolids solids contents of 35% and 40% respectively. Rehydration dilution by mixing process water back in to reduce the biosolids content back to 22.5% and 25% respectively, upon evaluation, produced a pumpable fluid at 4,847 cP and 5507 cP respectively, col 8, which viscosity was further reduced by mixing in further water (20% and 22.5%, col 10). In this example, pumpability at the expressed viscosity was achieved with no or only very minor reductions in the biosolids content of the initiating 25.6% material.
As shown in row G, a first preferred embodiment, the sample at 25.6% BS was heated on a hot plate with a temperature setting of 180 C for periods of 3 and 2 hours, col 3, respectively, to achieve an end Cake solids content of 40% and 50%, col 5. As in cols 5 and 6, this end Cake was rehydrated and diluted back to 20 and 25% by mixing and pumpability evaluated, col 8, at 5,039/cP and 5613/cP. In this case viscosity was shown as rising by the next day, with 1 sample rising to 27,000/cP, an unpumpable result. Further dilution to 22.5% again reduced the viscosity to pumpable ranges which held for the then-following next day, while continuing to rise. It is noted that hot plate heating resulted in wider variation in results which were alleviated in part by a spatula mixing.
As shown in rows H, P4.1, P4.2, U and Q, a first preferred embodiment, heating BSC of 24 and 25% solids at elevated oven temperatures for short periods (col 2 and 3) resulted in End Cake Solids of 45 to 70%, col 5. Upon dilution as shown in col 6 and mixing, col 7, in each case a readily pumpable viscosity was obtained, col 8. In the case of row P4,2 the low viscosity degraded by the next day, i.e. to 8,500 cP.
The individual elements of the first embodiment shown in
A second preferred embodiment is shown in
The results shown in
A third preferred embodiment provides a controlled process as in the first embodiment with the additional steps of the addition of a hydrolyzing agent, preferably time, to the re-watering step plus a period of heated incubation after the hydrolyzing agent (lime) is mixed in. Details of the operation of the third embodiment are shown in
In row J of
In row K of
In row M of
In the
Further processing steps of water dilution on the next day upon evaluation further reduced the viscosity each time as shown in columns 11 through 17. In summary, in each of the row M cases an initial Biosolids Cake having a biosolids content of 25.6%, a solid, has been rendered pumpable at an elevated biosolids content and very pumpable, i.e low viscosity, at its original biosolids concentration of 25%.
In row V a 400 g mass of 25.6% BSC was heated and dried in a convection oven set at 200 degrees Celsius at atmospheric pressure for 3.5 hours to produce a Dried Biosolids Cake with After Cook Solids content of 50%. Mixing and diluting in the presence of added Cal85 lime at 2, 3 and 4% with dilution to the equivalent of 35% biosolids content to form a RDBSC plus incubation at 99 degrees Celsius for 2.5 hours, upon evaluation, produced a pumpable liquid at less than 6,000 cP upon the further steps of dilution to 30% and 28%, plus evaluation, as shown in columns 13 through 15 (ND=next day value).
A graphical summary of the operation of the third preferred embodiment is shown in
A fourth preferred embodiment provides a controlled process as in the third embodiment wherein heating is provided by microwave energy and is detailed in the table shown
In this embodiment, S1, 400 grams of Biosolids Cake at 24% was microwaved for 5 minutes to a dry condition (approximate solids content of 47% based on the 24% Biosolids Cake figure), i.e. dried by ½ of the solids content. Addition of Cal85 time at 2.81% (based on the 24% Biosolids figures), dilution to a biosolids content of 20%, mixing for 2 minutes and incubation for 1 hour at 95 degrees Celsius resulted in a pumpable liquid with an initial viscosity of 4037 cP, which is noted to rise over the course of the next day but still pumpable.
In this embodiment, S2, 350 grams of biosolids at 25% was microwaved for 12 minutes to a solids content of 47% based on the 24% BSC figure, i.e dried by approximately ½ of the solids content. Addition of Cal85 time at 3% (based on the 25% BS figures), dilution to a biosolids content of 22.5%, mixing for 1 minute and incubation for 1 hour at 95 degree Celsius resulted in a barely pumpable liquid with an initial viscosity of 9000 cP. Further dilution to a biosolids content of 20% reduced the viscosity to 4415 cP.
In this embodiment, S4, 416 and 500 grams respectively of Biosolids Cake at 24% was microwaved for 18 minutes to a dry condition (approximate solids content of 47% based on the 24% Biosolids Cake figure), i.e. dried by ½ of the solids content. Addition of Cal85 lime at 4% (based on the 24% biosolids figures), dilution to a biosolids content of 25%, a more aggressive mixing as by a blender in a blender for 1 minute and incubation for 3 hours at 95 degree Celsius resulted in a pumpable liquid with an initial viscosity of 2010 and 2310 cP, respectively, which is noted to rise over the course of the next day but stilt pumpable.
In this embodiment, S52 and S6, 400 grams of BSC at 24% was microwaved for 13 minutes to a solids content of 50% based on the 24% BSC figure, ie dried by ½ of the solids content. Addition of Cal85 lime at 5% (based on the 24% BS figures), dilution to a biosolids content of 25%, a more aggressive mixing as by a blender in a blender for 1 minute and incubation for 3 hours at 95 degree Celsius resulted in a pumpable liquid with an variable initial viscosity of between 2771 cP and 6849 cP.
At tower temperatures and times this preferred embodiment of the process may require original (first) re-watering to a biosolids level lower than the original biosolids level but in any event at biosolids content of 20% or more.
A graphical summary of the operation of the fourth preferred embodiment is shown in
In each case a Biosolids Cake sample was air-dried at 35 C for 18 hours to dry from Biosolids Cake 24% through to a Dried Biosolids Cake at 67% and 59% as shown in column 5. Re-watering dilution back to 24% biosolids for a RDBSC plus aggressive mixing (as by a blender) for 30 seconds, for the cases of both Cal85 addition or not, column 7, upon evaluation, provided a range of BS content for 6,000/cP pumpable liquid ranging from 21% through 32% depending on incubation times of 0 (no incubation) and 95 degrees Celsius for 3 hours and presence or absence of Cal85 in the mix, see column 9.
The second step in the drying process in this embodiment was provided by thermal drying which dried the sample weights further to 139 and 180 gram weights respectively (as set out in column 3) for a 90% biosolids content by removing the amount of water set out in column 3a from the sample.
Batch rehydration by mixed-in water addition to the levels shown in column 4 (35, 40 and 45%) with each of Cal85 lime addition and incubation for 3 hours at 95 degrees Celsius resulted in evaluation levels as pumpable liquids with the viscosities shown in column 8. Aggressive intermixing of the reconstituting water, the cal85 and the dried Biosolids Cake (90%) was included in the process by mixing for 1-2 minutes as shown in col 6. A further included step of incubation for 3 hours at 95 degrees Celsius (Column 7) following or together with the intermixing steps showed evaluations with improved pumpability as shown in col 8.
Further embodiments include the product and procedure wherein:
at least part of the first step is carried out under vacuum, and,
the first step consists of a non-heat or unheated drying step followed by a heated drying step. In this case the unheated drying may be carried out by air drying at ambient temperature and pressure, dehumidication, and drying with only slightly heated sources. and
any alkali is sufficient to maintain the mixture at a pH of greater than 11, 11.5 and/or 12 during the thermal treatment first step. and
where the alkali dose rate is greater than 20 Kg time (CaO) and/or preferably 30-40 Kg per Metric Ton biosolids having a solids concentration of 24% W/W. and
the alkali does rate for treatment of biosolids cake is proportional to cake solids concentration. and
sources of alkalis and other than lime are used at dose rates based on their OH equivalence to time. and
the first drying step is replaced by acquisition of previously dried biosolids products and pellets. This dried material is processed in steps (b) and (c). and
a preservative other than alkali is added to the product to inhibit microbial growth at any one or more of;
(1) first step drying,
(2) second re-hydration step
(3) after re-hydration.
The scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations, and/or additions to the present subject matter as would be readily apparent to a person skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1805887.5 | Apr 2018 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2019/050427 | 4/9/2019 | WO | 00 |
