CA2241394A1 - Process for converting paper residues to fertilizer - Google Patents

Abstract

A process is disclosed for converting shredded money and food stamps withdrawn from circulation into a fertilizer compound, namely a pumpable fiber mulch including nitrogenous plant nutrients which can be applied to the soil as fertilizer. Finely chopped currency or food stamp residues are digested with mineral acid and the resulting slurry is neutralized with ammonium hydroxide to produce pumpable slurries useful in hydraulic seeding.

Description

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FIELD OF THE lNv~!;NlloN

This invention relates to a process for the environmentally acceptable disposal of paper residues, particularly shredded paper currency and food stamps, by converting such residues to mulch having agricultural applications.

BACKGROUND OF THE INVENTION

(i) Use of Cellulosic Mulches in Hydraulic Seeding The establishment of turf by spraying a mixture of water, grass seed, fertilizer and cellulose fiber mulch, commonly referred to "hydroseeding", has rapidly gained acceptance by landscapers. The fiber mulch is made from recycled materials such as wood by-products or recycled newsprint and, to that extent, is an ecologically responsible technique. Using simple and powerful pumping apparatus now available commercially, a single person can operate a hydroseeding system to apply seed, mulch and fertilizer simultaneously to large areas on golf courses, ski slopes, in parks, etc., so that labour costs are low compared to other methods for establishing turf.

(ii) Disposal of Waste Food Stamps and Paper Currency Withdrawn from Circulation The efficient disposal of food stamps and shredded paper money which has been withdrawn from circulation (hereinafter referred to as "currency residues") presents a serious environmental problem. At one time, currency residues were routinely incinerated, but the U.S.
environmental protection agency has banned this procedure as a source of pollution. Burial of shredded currency in landfill sites is not an acceptable alternative, given the enormous volumes of currency residues produced annually and the ~llm;nl shing suitable landfill space available.

The problem of disposal of currency residues is far more difficult than for ordinary paper residues such as used newsprint since the former are, for obvious reasons, formulated to be highly water-resistant. In particular, currency and food stamp paper stock do not pulp well when agitated with water using the conventional pulping methods applied to waste paper or wood by-products.

We undertook a research project aimed at developing an environmentally friendly method for disposing of currency residues and shredded food stamps. It was an object of this project to recycle such waste products to save landfill space and, if possible, to convert these residues into a useful end product.

Consideration was given to converting currency residues into mulch for hydroseeding as a possible disposal technique to satisfy our objectives, but it soon became evident that conventional mulching would not work to produce a useable slurry. The "pulped" material contained many non-reduced solid inclusions and, when mixed with grass seed and pumped into the ground, would "mat" into a compact layer which failed to produce adequate growth.

We have since discovered that currency residues, shredded food stamps and, indeed, all kinds of waste paper products can be chemically reduced to a fertilizer component that may be~applied alone, or with added nutrients, to the soil.

SUMMARY OF THE INVENTION

With a view to achieving the objectives discussed above, the invention provides a process for preparing a fiber mulch from paper residues, for use in hydraulic seeding, comprising the digesting of a quantity of finely cut or chopped paper residues in a aqueous solution of mineral acid such as sulfuric acid, nitric acid or phosphoric acid, heating the acid/residues mixture until a slurry is formed which has substantially no rPm~;n;ng solid bits of paper in it and, after allowing the slurry to cool to room temperature, reacting excess acid with a strong aqueous solution of ammonium hydroxide to produce a pumpable slurry of fiber mulch.

The slurry of fiber mulch is useful in convention hydraulic seeding (hydroseeding) applications, particularly as the ammonium sulphate by-product of the mulch preparation is itself a plant fertilizer. The technique of heating the finely divided paper residues with sulfuric acid is effective in reducing otherwise intractable paper stocks, particularly currency residues and food stamp residues, so a root is provided to disposal of these waste materials.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The pretreatment of currency residue is of importance in effective digestion and pulping of the material with acid according to the present invention.
Currency residue is typically 1/16" x 6" shredded paper ("shred") which is visually recognizable as cut-up paper money in various denominations. This material must be cut or chopped to a fine powder. Grinding (as with a mortar and pestle) or milling (metal ball grinding machines) were found to produce a matted material which is much more difficult to digest than the original shred.

The particles of shred are digested with acid under conditions which produce a slurry containing few or no bits of shred. Sulfuric acid has proved to be the reagent of choice because of its price, low volatility and apparent efficiency in tearing apart cellulosic fibers.

Example 1 In prel;~;n~ry laboratory-scale tests, currency shred was heated with sulfuric acid (reagent grade conc.
H2S04) diluted with water in a glass vessel equipped with a reflux co~Aen~er. Conditions which produced a substantially homogenous slurry are given in Table I
below.

TABLE I
SHRED [H2S04] H2o Time Temp. ' Results () (mL) (mL) (h) (~C) 0.5 5 25 3 60-65 Slurry, few bits 0.5 0.5 10 3 Reflux Much finer slurry, no bits 2.5 1.5 20 1 Reflux As above Where the slurry is to be used as a hydroseeding mulch, the lower limit of acid is determined by the need for excess acid for subsequent reaction with added NH40H
to produce (NH4)2S04 at a concentration of 5~ or more.

The shred slurry can be pumped from the reaction vessel and subsequently air-dried on plates or on a rotating drum.

Example 2 The resistance of certain paper stocks to pulping was ~em~nstrated by soaking currency residue and food stamps at room temperature in "weak" sulfuric acid, namely, commercial automotive battery acid.

Very little dissolution of the currency residue was observed even after 26 days of soaking in the weak sulfuric acid. The food stamp residue was found to be only slightly more susceptible than currency residue to dissolving in weak sulfuric acid.

Example 3 To 2.5 Kg of shredded currency was added 1.5 litres of concentrated H2SO4 (-95~). To this mixture, twenty litres of water was slowly added with stirring. The mixture was heated to the boiling point, then allowed to cool to room temperature. The pH was reduced to 5.5 by the addition of a concentrated aqueous solution (~28%) ammonium hydroxide, which required about 4.0 litres.
This was found to produce a pulpable slurry having a high nitrogen content of about 22%.

Example 4 The hydromulch of Example 3 was field tested at a number of sites and was found to produce comparable results, in bringing up grass to conventional wood by-product and waste newspaper mulches.

Example 5 The procedure of Example 3 was repeated using 1.0 Lof concentrated nitric acid instead of sulfuric acid.
This produced a pulpable slurry with a significantly higher nitrogen content than that of Example 4.

Example 6 The procedure of Example 3 was repeated using 1.0 L
of concentrated phosphoric acid instead of sulfuric acid.
A pulpable slurry was obtained after neutralization with ~mmo~;um hydroxide which contained both nitrogen and phosphorous, which are essential minerals for plant growth. This slurry was easily blended with slurries produced in Examples 4 or 6 to produce a balanced fertilizer mulch containing the optimum ratio of-nitrogen and phosphorus for the desired application.

From these examples it will be seen that shredded currency and food stamps, which are highly resistant to break-up into a tractable mulch by conventional techniques can be transformed into a fiber mulch which contains plant nutrients for use in hydraulic seeding, thereby addressing the serious disposal problem for such waste paper materials, while converting them into useful agricultural end product.

Claims (3)

1. A process for preparing a fiber mulch from paper residues, for use in hydraulic seeding, comprising the steps of:

(i) cutting or chopping a desired quantity of said residues to a fine state of division;

(ii) adding an aqueous solution of mineral acid to the cut or chopped residues in a reaction vessel;

(iii) heating the acid/paper residues mixture to produce a slurry containing substantially no solid bits of paper; and (iv) allowing the slurry to cool to room temperature and reacting excess acid with a strong aqueous solution of ammonium hydroxide to produce a pumpable slurry of fiber mulch including ammonium salt of said mineral acid.

2. A process according to claim 1, wherein said paper residues are selected from the group consisting of currency residues and food stamp residues.

3. A process according to claim 2, wherein said mineral acid is selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid and mixtures thereof.