FR2622568A1 - Compost of wood sawdust and purification station sludge - Google Patents

Abstract

Composting process employing urban purification station sludge and wood sawdust. Composting process making it possible to manufacture a compost from the mixture of sawdust and urban sludge with the aid of a hydraulic shovel or of a bulldozer arranging them in swathes turned over every month according to an established process and in proportions varying from 1 to 3 m<3> of wood sawdust mixed with 1 m<3> of sludge. The temperature rises make it possible to keep down many weeds and most of the pathogenic germs. The compost dries naturally, provided that it is brought back under roofing before the end of the maturing. The compost obtained can be marketed in bulk or in bags and is intended for the cultivation of flowers, vegetables, parks and gardens by virtue of its low pH, the richness of its components and its microorganisms.

Description

The invention relates to the manufacture of a potting soil from two main materials: sawdust and sewage sludge.

The sawdust produced by the sawmills in our region is sometimes sold to Belgian industrialists (manufacture of briquas etc ...) or given to farmers to cover their silos or quite simply abandoned.

The sawdust usually used in our region has a C / N ratio of around 400 (generally poplar). Such sawdust used in the pure state would cause a depressive state of the plants. All kinds of sawdust are suitable for this process.

Wastewater treatment plant sludge (of the order of 10-12% dry matter) contains microorganisms which degrade the cellulose contained in sawdust. In addition, they have the advantage of providing nutrients to the final product.
N, P, K, Mgo, Cao. All types of sludge are adaptable even limed sludge. However, if the sludge used has too high a loor metal content, the use of compost would then be prohibited on vegetable crops.

The evacuation of sludge from wastewater treatment plants is generally a big problem for cities, hence the interest of this inexpensive process.

In our region of northern France, horticulturalists generally use blond peat or other products almost all imported from Belgium, Holland or Germany and often inert products.

The soil obtained by this manufacturing process has the advantage of being a living product thanks to its microorganisms;
The agronomic value of the product is seen from different aspects:
- the richness of the product in interesting elements for agriculture = organic matter content and fertilizing elements, this is given by the chemical analysis of the product.

- the effect of compost on plants (pot culture test with tomatoes.

- ~ the physical and chemical properties of the compost, properties which condition the use of the product as a growing medium (pH, salinity, porosity, water and air contents).

In addition, its fairly low pH (5.5 to 7) is interesting in horticulture. Its C / N ratio of around 15 to 35 shows a mature product.

Chemical analysis of the soil
:: 30 to 70%
organic matter: 10 to 45
pH: 5 to 7.5
Total limestone 0 to 20
Kjeldahl nitrogen 4 to 30 O / oo
Total phosphoric acid HF: 1 to 5%
Total potassium HF: 1 to 5%
Total magnesium HF: 0.2 to 0.5%
C / N: 15 to 40
PRINCIPLE
Aerobic microbes need nitrogen to break down lignified cellulose-rich residues; this nitrogen is supplied by the sludge.

Their activity depends closely on the temperature; they are very resistant to cold; their development is maximum for a temperature of 30,400.

Humidity is an essential factor in their activity.

The reaction of the medium (pH) which is most favorable to them is neutrality or a very slight alkalinity. (sludge pH greater than 7).

MANUFACTURING PROCESS :
The sawdust comes from the surrounding sawmills and is transported by dump truck in a cordon on the ground (Fig 1) (1) or in a silo (Fig 2) (1).

The silo principle (Fig 2) is preferable in order to avoid the overflow of sludge. This sawdust (1) is then spread using a bulldozer. The sludge from the treatment plant (2) is also transported by sealed tipper truck directly from the treatment plant daily and is dumped on the sawdust in the ratio of 2 m3 of sawdust to 1 m3 of sludge. This ratio can vary depending on whether you want a richer or less rich final soil.

The first installation 61 performs as follows:
- A hydraulic excavator (3) takes: the spread of sawdust (1) covered with mud (2) and by mixing it makes the windrow B which is a first mixture which is still coarse and not very consistent.

- If the ground on which the operations are carried out is sufficiently load-bearing (concrete areas for example), mixing and turning can be carried out using a dozer loader commonly called a wheel loader.

- One month after the pile B will be moved making a pile C and so on each month until complete maturity of the compost occurring from 9 to 10 months after the first installation.

The interest of the turnings is to aerate the mixture and with the help of nitrogen thus nourish the aerobic microbes which will decompose the carbon products. A few days after turning the temperatures rise to reach temperatures of up to 60-65 under certain conditions which will lead to the disappearance of many weeds and pathogenic germs. Then the temperatures will drop again, which is why the piles will have to be turned over again. This will again allow the temperature to be raised by aerating the pile and thus accelerating carbon degradation.

It is desirable to make windrows not too high and not too bulky in order to avoid compaction which is harmful to air circulation.

Turning over each month seems to be a good compromise for a good ratio of production speed / cost price.

As the product approaches its final state, it becomes more consistent, its temperature drops and the volume decreases sharply. In a particular case of implementation, if at the start we had 3 m3 of sawdust plus 1 m3 of mud at the end of the circuit, there will only be approximately 1 m3 of soil left.

The manufacture of the compost being finished, the heap no longer heated, and the C / N is then less than 40.

The soil then returned to the shed, crushed, and naturally dried. It is advisable to bring it in a little before the end of maturation in order to dry faster thanks to its temperature.

The dry matter content of the soil can vary.

The soil will then be delivered in bags or in bulk. It is a clean product, odorless.

Its density may vary depending on its dry matter content, but is generally around (5) to 1 oon S m3.

INTEREST OF THE LAND
- Agronomic benefit: Experiments carried out from the beginning of 84 in horticulture highlight the qualities of the product: early flowering, stockier and healthier plants, less susceptible to diseases, having better rooting and saving on fertilizers.

A memoir published in December 84 confirmed these characteristics: good resistance to drought, stockier and healthier plants, savings in fertilizers, reduced susceptibility to diseases.

New tests carried out in 1985 confirmed the economic and technical interest of this product.

- Ecological interest:
Use of waste (sludge, sawdust) and by-products.

Natural fertilization
Elimination of nuisances due to the storage and discharge of wastewater treatment plant sludge
Use of sawdust sometimes abandoned.

- Economic interest:
By the low cost of recycling sludge from wastewater treatment plants.

USES
The outlets are horticulture, parks and gardens, market crops, individuals, amateurs and professionals.

MARKETING:
In bags or in bulk
At the request of certain users, the product can be marketed as a mixture with blond peat imported from natural peat (Pas de Calais peat bog for example), which have the advantage of lightening the product and lowering the pH, to offer a ready-to-use product, to lower the cost price without compromising the quality of the product. The 50% peat 50% potting mix seems a good mix.

Claims (12)

1. Composting process using sawdust and sludge from municipal sewage treatment plant, characterized by the following steps: a) the sawdust is spread using a bulldozer on the ground or in a silo. b) sludge from municipal sewage treatment plants is dumped on sawdust. c) the sawdust and sludge are then mixed and then placed in windrows and turned over. 2. Method according to claim 1 characterized in that the turning is carried out with the aid of a hydraulic excavator or a loader dozer, 3. Method according to claims 1 and 2 characterized in that the turning is carried out once a month. 4. Method according to claims 1-2-3 characterized in that the proportions of the mixture vary in the following ratios: 1 to 3. m3 of sawdust mixed with I m3 of sludge. 5. Method according to all of claims 1 to 4 characterized in that the dry matter content of the soil can vary from 30 to 70%. characterized in that the density of the soil can vary from 600 to 1000 Kgs per cubic meter. 6. Method according to all of claims 1 to 5 7. Method according to all of claims 1 to 6 characterized in that the soil dries naturally on the condition of being returned to a shed before the end of maturation. 8. Method according to all of claims 1 to 7 characterized in that the obtained potting compost is clean and odorless. 9. Method according to all of claims 1 to 8 characterized by the following chemical analysis Ms: 30 to 70% organic matter: 10 to 45 pH: 5 to 7.5 Total limestone 0 to 20 Nitrogen kjeldhl 4 to 300/00 Total phosphoric acid HF: 1 to 5% Total potassium HF: 1 to 5% Total magnesium HF: 0.2 to 0.5 A C / N: 15 to 40 10. Method according to all of claims 1 to 9 characterized in that the soil obtained can be marketed in bulk or in bags, alone or as a mixture with peat or the like. 11. Method according to all of claims 1 to 10 characterized in that the weeding and disinfection taking place on condition of obtaining T of 60-65. 12. Method according to all of claims 1 to 11, characterized in that the soil has reached maturity when the C / N ratio is less than 40.