Cases study

Industrial paper mill in Bulgaria: Design and implementation of a multiple-step equipment with 4 treatment units

Analysis, design and implementation of a new multiple-step hybrid plant in a paper mill in Bulgaria

Field of activity

Field of activity


“Pulp” production: a bleached natural pulp deriving from tree species used for the production of various types of paper (e.g. tissue paper, printing paper, cardboard,…)

Location of the plant

The production premises are located 3 km from the centre of Svishtov (Bulgaria)

Emission problem

The overall plant has more than 35 emission areas. However, the ones coming from the vacuum evaporation process are causing an olfactive nuisance in surrounding areas

Service supplied by Labiotest

Design and implementation of a new plant

Type of action

Installation of a multiple-step plant with 4 treatment units

In 2014, a Bulgarian paper mill contacted us. This company is a leader in its field, specialized in the production of “bleached Kraft paper”, using a pulp deriving from local tree species. 

This ECF bleached pulp is used as raw material for the production of various types of paper: 

  • Tissue paper 
  • Writing, printing, copying paper
  • Paper with a pigmented covering
  • Undulated cardboard with a covering
  • Cardboard 
 The emissions deriving from one of the production processes were strongly perceived by the local population, also creating critical conditions for the workers themselves.


The factory as a whole had more than 35 emission areas, but the most difficult situation regarded emissions coming from the vacuum evaporation process that caused an olfactive nuisance in the surrounding areas. 

The olfactive impact of emissions coming from both «vacuum evaporation» areas, even though having a limited total flow rate (8.000 m3/h), was perceived by the population in the nearby city of Svishtov, and created a difficult situation for operators themselves. 

We started with performing a series of olfactometric and chemical analyses, in order to know more about these emissions and their characteristics. 

Phases of the intervention

1. Tests with a pilot plant

As pollutants perception thresholds were low, in order to guarantee the olfactometric result, it was necessary to ensure very strict analytical guarantees:

First of all, we offered setting up a 500 m3/h pilot system simulating a multiple-step treatment for 2 days, in order to ensure some characterizations of the air upstream and downstream of every step, thus getting a well-detailed protocol of the measurements we would have performed during the 2 day-test. 

It was thus possible to verify equipment efficiency, and implement it to obtain the targeted results.

At the end of the experiment, we delivered a detailed report with the test measurements results, as well as a small summary of efficiency rates achieved for each treatment step: 

2. Design and implementation

This pilot phase allowed offering the customer the most suitable technology that would meet with expectations and requisites. 

After a thorough verification of available overall dimensions and technical feasibility, we offered multiple-step equipment based on an abatement process including 4 treatment steps: two wet steps and two dry ones.

  • Phase 1: Wet scrubber: H2S abatement and part of COT dissolution
  • Phase 2: Demister unit: liquid fraction and water-soluble substances abatement through coalescence
  • Phase 3: Dry chemical-physical scrubber: COT and residual H2S abatement
  • Phase 4: Wet scrubber: COT and residual organic sulphur oxidation and dissolution 

3. Implementation and testing

Our technicians implemented and started the equipment directly, in an accurate and competent way. Finally, during the testing phase, the following actions were performed:
  • H2S measurements with the help of bubblers (solution with a known ratio of zinc acetate) upstream and downstream of the equipment. 
  • COT measurements upstream and downstream of the equipment with FID.

This allowed delivering a detailed report with analyses results: the equipment was operatimg and set up perfectly, in order to guarantee the best performances and efficiency rates required.


The plant met with efficiency requisites. Therefore, it was approved as a final solution to malodorous emissions problems. Today, the population of Svishtov does not perceive any olfactive nuisance coming from the production process of the type of paper mill «pulp» taken into consideration.