Use of zeolite inside fermenters

Zeolite is a natural mineral of volcanic origin with high porosity and high surface area that acts both as a molecular sieve, trapping molecules and particles with diameters larger than the zeolite channels, and as a cation exchanger.

Zeolite can be used to treat the ammonium problem in biogas plants. In particular, it can be used:

  • In the reactor: the toxicity of ammonia towards microorganisms inhibits methanogenesis.
  • In liquid digestate: for the agronomic use of organic matrices for fertilising purposes, the maximum annual limit for nitrogen input from livestock origin is 170 kg per hectare (Directive 91/676/EEC).

Zeolite inside fermenters can perform the following functions:

  • Support medium for microorganisms: increase of microorganisms and growth of their activity;
  • Ion exchanger to reduce ammonium peaks (NH4+) and heavy metals;
  • Containment of odour emissions;
  • Reduction of the hydraulic retention time (HRT) of the biomass;
  • Filter media: to treat the outgoing liquid digestate, which is then recirculated in the system – saving water and micronutrients.

 

Zeogas: a micronised natural zeolite product for use in biogas plants

Zeogas is a micronised natural zeolite product with high ammonia selectivity for use in biogas plants.

Physical properties:
– Clinoptilolite-based granular zeolite
– Micronised powder < 200 microns
– Cation Exchange Capacity: 150 cmol(+)/Kg

 

Case study – Zeogas for ammonium removal in bioreactor

General data of the plant
In a recent case study, a biogas reactor was treated with biomass inputs from livestock residues and thus susceptible to the problem of ammonium peaks. Seventy-five kilograms per day of Zeogas product were used for an ammonium concentration of 10000 mg/kg in a 2000 m3 fermenter, fed with 18 tonnes of biomass per day.
After 7 days of contact, the ammonium concentration drops from 10000 ppm to 7500 ppm.
After 14 days, the ammonium concentration reaches about 4000 ppm, and the use of zeolite is discontinued.

Biomass treatment with zeolite to reduce ammonium peaks

 

The use of 1 tonne of zeolite (75 kg per day) within the bioreactor ensured an ammonium abatement of > 60% during this period.
The amount of zeolite used to break down the ammonium peaks is therefore 3.8 kg of zeolite per tonne of biomass (0.4 wt%).

 

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