start-up and seeding

Seeding is always required when the unit is started up. For the Anaflux, the quantity of biomass to be added by seeding is relatively low ; depending on the size of the reactor, generally between 10 to 20 m³ of granular sludge should be allowed for. For granular sludge reactors, significantly higher quantities are necessary; in this case, the higher the quantity of biomass added, the shorter the startup time, especially when:

• the biomass is already adapted to the pollutants to be treated (supplied by a unit working on the same IWW);
• the biomass is available in appropriate form; for instance, in granular form for granulated sludge blanket devices.

When seeding is not available or available but in small quantity, it is recommended to increase the loading gradually; in effect, with relatively high losses in sludge (due to acclimatisation) and low micro-organism synthesis (0.1 to 0.2 kg VM per kg of BOD₅ eliminated), it may take several months to increase the load!

To reduce the cost of transportation, centrifugation or filtration (GDE, Superpress) can be used to thicken the sludge. These operations must be controlled (storage period, polymer dosage, etc.).

After a reactivation period of a few days (for temperature stabilisation), a COD loading of approximately 0.1 kg · kg^–1 VM · d^–1 should be applied; it is then gradually increased, to maintain a VFA/TAC ratio of less than 0.2 and a pH of close to 7. It is reasonable to expect to double the loading every 10 to 20 days, depending on the nature of the effluent and the process used.

nature of the seeding sludge

When acclimatised sludge is not available, the following can also be used:

• UWW digested sludge;
• livestock refuse (cattle, pigs).

The following parameters are used to check the characteristics of sludge before collection:

• the mass flow rate removed in the original reactor;
• specific gas output; m³ of gas per m³ of reactor and per day;
• pH and operating temperature;
• % VS in sludge.

quantity of sludge required

• Analift: from 3to 5 kg of VS per m³ of reactor.
• Anapulse: 20 to 60% of the reactor’s capacity in granular sludge (depending on time available for start-up).
• Anaflux: ~ 5 % of the reactor’s capacity.