Draft of the BAT finishes discussion on the membranes

2016-09-20 00:00:00

Draft of the BAT finishes discussion on the membranes

Baseless and moreover false informations about using of membrane systems in waste biological treatment are circulating for a certain period in the environment industry. Therefore let us sched a light on this issue by citing the provisions of the current BAT project, which clearly indicates
the semipermeable membrane as one of the best available techniques in closed systems.

Joint Research Centre of the European Commission (JRC) published in the December 2015 draft
of BAT (Best Available Technique) Reference Document (BREF) on the best available techniques for waste treatment. This project is the result of several years of work of the Technical Working Group (TWG) at the European IPPC (International Plant Protection Convention) Bureau in Seville. It regulates precisely among other things, the issue of the use of closed membrane system for biological waste treatment.

Technical description

Chapter of the document mentioned above describes encapsulated facilities
with semipermeable membrane, as commonly used in waste aerobic treatment. Membrane systems are divided into three categories according to the degree of design complexity and related capital expenditure:

1. Designs requiring devices to move a cover:

a. heap version with cover sealed to the ground;

b. sidewall version with cover sealed to the sidewall as well as to the pushwall.

2. Structural designs with semipermeable membrane laminates mounted to a moveable

frame construction:

a. butterfly version

b. lifting roof version with a common wall.

3. Combined designs:

a. closed flexible encapsulation connected to a negatively aerated building (feeding tunnel).


The described technology is based on functional component, which is semipermeable membrane,
and the liquid condensate layer being generated on its inner surface which acts as a bio washer.
The combination of these two elements enables the effective dissolution of gaseous substances,
the reduction of emissions of volatile organic compounds, dust or ammonia.


The input material that is encapsulated with the semipermeable membrane is protected both from excessive moisture, as well as against rapid drying due to the hydrophobic properties, moisture and air permeability by using temperature and / or oxygen sensors, which control treatment process under the membrane.

Tightly closed


For the proper functioning of the aerobic treatment and emission reduction, it is necessary to have the input material in a closed environment, regardless of the selected design option. All versions supplied by EQUIPO are designed so that the connections between the cover laminate and the choosen design ( example 1,2 and 3) (the interfaces between the ground
or sidewall and pushwall or the common wall to the cover) are sealed to avoid bypass streams.

In the option with sidewalls the membrane with a framing edge strip (non-permeable) is sealed
to the top of properly prepared walls, utilising e.g. clamps, flexible ropes, which provide tight cover
for whole heap. It should be emphasized that the sidewalls must be adapted to seal the membrane, their structure must allow tight adherance of the laminate to ensure tightness of the process. For this reason walls require special design, they should also be covered by professional means increasing adhesion of the laminate in contact points. All of this can be ensured by experienced, sustainable suppliers of the leading membrane solution for almost two decades.

Emission abatement

Encapsulated, positively aerated facilities covered and sealed with semipermeable membrane covers are a common method of treating emissions, such as odours, ammonia, VOCs, dust and bioaerosols from an active composting heap.


Table 4.56: Emission abatement as Cover Efficiency and vs Baseline Factor of semipermeable membrane covers


Emission type

Cover Efficiency

vs Baseline Factor




90–97 %(1, 2, 3)




99.99 %(1,3)



Dust/particulate matter (4)

99.99% (4)







80 %(5,6)



90–95 % +(7)


90–98 %(7)


(1) [ 132, Kühner 2001 ].

(2) [149,Kühner 2000.]

(3) Input: Bio-waste; measurements carried out with the same product as (6).

(4) PM 2.5 Particle Filtration efficiency according to 'VDI 3926, Part 2 Testing of Filter Media
for Cleanable Filters under Operational Conditions from December 1994'. This test was carried out on GORE® L3650 which is a Dry Filtration Media with an ePTFE membrane with a much wider porous structure. This is only for indication purposes. The performance of the GORE® ePTFE

membrane of GORE® Heap Cover is supposedly much better due to the tighter pore structure
and the fact that a dry filtration test represents a worst case scenario. The trapping effect of the aqueous condensate film for fine particles cannot be considered with this test.


(5) [ 133, Schmidt et al. 2009 ].

(6) Input: BioSolids/Sewage Sludge; measurements carried out with GORE® Heap Cover
with semipermeable GORE® ePTFE membrane.

(7) Measurements with different input materials in the framework of a project to prove GORE® Heap Cover as BACT (Best Available Control Technology) according to SJVAPCD (San Joaquin

Valley Air Pollution Control District; CA) Rule 4565 and Rule 4566 and SCAQMD (Southern California Air Quality Management District; CA) Rule 1133.


The performance of encapsulation with semiperrmeable membrane covers, in the respective case design version 1b of, achieved odour control similar to or better than conventional tunnel composting systems with a biofilter and subsequent maturation for a site with an annual capacity
of 60 000 tonnes of a mixed waste input of 70 % bio-waste and 30 % green waste. [134, BRUYN]


With respect to Green house gases, there is also a comprehensive case study available (German Environmental Prot. Agency, 2009, emission control) that confirms the performance (CO2 Equivalents)  with 12 Kg/ton per input material for the membrane technology. This evaluation also states, that a comparable Tunnel solution is performing with 47 Kg/ton (Methane, Amonia, Laughing Gas…). On a total view on a plant this gives a clear and doubtless indication on the power of the membrane technology.


Environmental benefits and aims of implementations

If the two technologies (membrane vs. tunnel) were to be compared a significantly lower investment in both, the operation and investmenet costs have to be mentioned.The simple and robust design allows an incomplicated extension of the treatment capacity for future needs of the plant. In order to maintain the membrane in good condition it is recommended to use devices directly dedicated to unwinding and winding of the membrane, using of best practices ensures membrane life expectation on an average on 7 years (up to 10 years) on a proven track record.

Achieved environmental benefits

  • Low energy consumption: 1,5–4 kWh/t of input material (depending on the design and type
    of aerobic biological treatment).
  • Emission reduction without further exchange of media (no depletion) like in the case
    of biofilters
  • No inherent odours generated by the semipermeable membrane cover.
  • Lowest carbon dioxide equivalent compared to other technologies for composting operations



Reference installations


EQUIPO Sp. z o. o.

Zbąszyńska 4
91-342 Łódź
TAX-ID: PL7272794609
tel. +48 42 235 28 33
fax. +48 42 235 28 24

EQUIPO Sp. z o. o.

Zbąszyńska 4
91-342 Łódź
TAX-ID: PL7272794609
tel. +48 42 235 28 33
fax. +48 42 235 28 24