The MV82 plant (STP)- The plantation

The septage treatment plant MV82’s filtrates are absorbed during the summer (6 to 8 months per year) by a poplars and eucalyptuses plantation whose wood production feeds Nègrepelisse’s communal heating system. An innovative operation on the treatment and energy project.

 

Goals

Two main functions:

• export (by infiltration in the soil and especially by water lose) the septage filtrates, too much polluted to be rejected in the receiving water
• encourage (by water and nutrient contribution) the trees growth and therefore the wood-energy production.

Vegetable’s choice

From the many vegetables of the beginning, four were eliminated during the study:

1. the “miscanthus” because it could proliferate and it isn’t scientifically known very well (no studied French plant and very little results from the studies abroad)
2. the locust tree because the species doesn’t improve the water contribution
3. the bamboo because it’s expensive to plant and to garden
4. the willow as Short Rotation Coppice-SRC because of the upkeep constraints (cutting every two years) and inappropriated to the weather.

Forest tree species as Short Rotation Coppice-SRC (poplar, eucalyptus, sequoia…) were chosen because of the good results registered by FCBA after twenty years of continuous using (only plantation, without the wastewater spreading). Economical and simple solution justified by the local forest keepers’ experiences and FCBA. Interesting regarding it’s developments because the cutted woods are used by different users with an offer lower than the demand.

Chosen tree species, regarding the plot’s weather conditions:

• poplar: “cultivar Dorskamp » registered in the catalog and recommended for the south-east zone according to the cultivar poplars’ regionalized list with state’s assistance
• eucalyptus: hybrid cultivar gunnii x dalrympléana  from the species- clone 208.

Short Rotation Coppice - SRC

The SRC method consists of denseness tree species planting (1250 stems per acre), which grows from the stump after cutting. The wood is mechanically “harvested” with currently used machines in Europe and which makes blocks usable in a heating system. The trees grow back by themselves after cutting.

The SRC tree species are usually developed in energy biomass (burning in adapted or ordinary heating system since antiquity) and in paper industry (pummeling since the beginning of the twentieth century), as well as in particle panels with the wood industry. The long practice and the success of these developments with industries and particulars guaranteeing their investments, since the offer is lower than the demand, in France and in the world. The fossil fuels reducing strengthen this tendency short, medium and long-term.

Watering

Several techniques can distribute the septage filtrates on the plantation: ???? micro-sprinklers, calibrated nozzles, drop by drop.

The calibrated nozzle technique, kept after comparative studies distributes water with a pipeline system with a weak pressure ( 0.3 to 1 bar at the implement point), buried (in the upstream parts) or on the ground (in the downstream parts) and applies it at the plant’s level by a calibrated opening (an “nozzle”) from 1 to 2 mm diameter supplying a little depression digged at the plant’s foot with a 2 to 30l per hour rate of flow .

Advantages:

• good distribution with the parameters adjustments (successive diameters, pressured supplying, big surface areas’ division)
•  weak clogging risk (under pressure distribution, quite big holes), weaker than with micro-sprinklers or drop by drops after specialists advices
• easy running with clean an waste waters.

Biomass production

Dry production on 5 acres: around 400 DT (dry tons) by rotation, ie 50DT/year for an eight years rotation. Similar values for the poplar, the eucalyptus and the sequoia.

The septage filtrates watering increases the woody production in a still unknown proportion.

Schedule

The plantation itself was done in the spring 2011 on the cadastral lots ZH93 and ZN193, SMDD’s property. The watering system and the general constructions (fence, pathes…) will be done in the same time as the septage treatment unit.

Consult
all files's list