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The textile&fashion industry in Europe is represented by 172.756 companies, with an average of 9 employees per company, often located within highly populated areas. Interestingly, starting from the late nineties, an innovative textile printing technology has emerged: digital (or “ink-jet”) printing. Considering the (most advanced) district of Como (Italy), 58% of the printed textiles are now manufactured using Digital Textile Printing (DTP). Even if economically (and, partially) environmentally better performing than traditional textile printing, for technical reasons DTP is responsible of an increase of more than 200% of nitrogen content in wastewater, resulting in a doubled sludge volume, doubled quantity of carbonaceous substrate and polyelectrolyte. In fact, the ink-jet printing requires other pre-treatment operations in addition to traditional preparation treatments, as a result of the different physical characteristics of the inks used compared to traditional printing pastes. DTP systems use low-viscous inks to attain high jetting frequency from small nozzles. This implies that some ingredients of the traditional printing pastes have to be put over the fabric before printing. In particular: urea, the ink fixer compound. Actually, DTP is thus a `two-phases’ printing as opposed to the `all-in’ approach of conventional printing: in the latter case, all the dyes, chemicals and thickeners required are included in the printing paste, whereas in the former some ingredients (urea) are applied in a new pre-treatment process. The problem is that such a pre-treatment contemplates the impregnation of 100% of the to-be-printed fabric (while in traditional printing technologies, just the areas covered with the ink are actually treated with urea). This drastically increases the amount of urea used per square centimetre of fabric. Urea is then (completely) washed out after printing and results as a pollutant in the company wastewater.
Major European textile districts are thus experiencing a drastic increase in the nitrogen content of their wastewater. WWTP collecting urban wastewater may have more than 50% of contribution from industry and, furthermore, textile industries are often placed in districts, where all the companies in the given area operate in the same sector.
LIFE DeNTreat aims at demonstrating that an innovative Anammox (ANaerobic AMMonium OXidation microorganism)-based, on-site wastewater pre-treatment module is able to sustainably abate nitrogen pollutants from selected points of discharge in order to reduce nitrogen content of overall urban wastewater, resulting in a re-established optimal operation of WWTP.
The Demonstration plant
1 – NOT TREATED WASTEWATER
The wastewater treated by the pilot plant comes from the equalization tank already existing end-of-pipe of the company discharges and is pre-treated through a basket filter to prevent the entry of any threads into the storage tank.
2 – FEEDING TANK
The tank is used to store and homogenize the wastewater to be treated, through a dedicated recirculation pump, and to regulate the temperature. This parameter is kept in the range 35°-38°C thanks to a cooling/heating system, consisting of a coil fed with service water for cooling, and a steam jet for heating.
3 – SBR
In the reactor the contact between wastewater and bacterial granules takes place. Being a batch-type process, it is structured in phases, whose complete cycles consist of loading, reaction, sedimentation, unloading and stand-by. The tank has a recirculation system for in-line measurement of chemical parameters and a nitrogen gas recirculation system for mixing. The tank is equipped with electric tracing and insulation to maintain the temperature, and with pressure, level and temperature gauges.
4 – GASOMETER
The gasometer is connected to the reactor by the nitrogen recirculation and is used as a volumetric compensation of the gas phase. It is equipped with a fan and a hydraulic guard to maintain the pressure in the reactor between 20 and 25 mbar.
5 – ON-LINE ANALYSIS
The chemical parameters are continuously monitored thanks to in-line measurements given by pH, dissolved oxygen, RedOx, ammonia and nitrates probes installed on reactor recirculation.
6 – REAGENTS
In the reactor recirculation system, reagent dosing points for pH and foam control are installed. In the feeding tank there is a phosphoric acid dosing point to satisfy the phosphorus request.
During the loading and unloading phases, the wastewater is sampled in order to carry out further analyses of the chemical parameters in the laboratory.
8 – TREATED WASTEWATER
The treated wastewater is discharged into two tanks arranged in sequence whose function is to avoid the accidental uncontrolled loss of biological sludge.
9 – PLC
The plant is equipped with automation and remote control system
General design data
Design flow rate: 40 m3/d
Operating flow rate: 10 – 40 m3/d
Influent concentration: 130 – 260 mgNtot/l; avg ± st. dev.: 176 ± 44
Target effluent concentration: < 50 mgNtot/l (5%-ile = 100 mgN/l); < 0,6 mgN-NO2/l.
|FILLING – Filling of Reactor SBR Anammox.
|REACTION – Reaction between bacteria and wastewater.
|SETTLE – Sedimentation of bacterial granules.
|DISCHARGE – discharge of the treated effluent.
|IDLE – Reactor in standby.
LIFE DeNTreat will sustainably abate the N content from polluting sources resulting in:
- a residual N content below 100 mg/l in the wastewater released in the collection system
- accomplishing Directive 91/271/EEC art.5 requirements asking to ensure that the minimum percentage of reduction of the overall load entering all urban WWTP in a given area is at least 75% for total nitrogen produced
- respect of residual nitrogen concentration in WWTP discharges, to be maintained below 10 mg/l
With the following impacts:
- an actual saving of up to 40% in investment and operational costs
- a reduction of the N2O emissions during biological wastewater treatment to less than 20% of the currently adopted technologies
- an abatement of the sludge produced as a result of the nitrogen abatement process to less than 25% of the currently adopted technologies.
STAGES AND ACTIONS
DeNTreat goes through four sequential phases: preliminary activities will complement data collected during the lab-scale study already performed by three of the project partners with further information aimed at fine-tuning the configuration and application context for the DeNTreat solutions. Secondly, the DeNTreat demonstration system will be designed, built, and run in a textile manufacturing company. In the third step, process performances in a real production environment will be assessed. In the last step, gathered information and achieved results are spread all over Europe through well-targeted dissemination and exploitation campaigns.
The final expected project outputs are:
- a pre-industrial wastewater treatment plant based on an Anammox bioreactor, TRL7, demonstrated in a representative operational environment processing 40 m3/day of wastewater
- a lab-scale pilot, based on the same technology as above, validated as a “portable clinic” intended to quickly test samples and provide a rapid quotation for industrial-scale treatment plants
- easily-deployable after-LIFE DeNTreat implementation methods and approaches aimed at facilitating the widest adoption of the technology in every European textile districts
The combination of the above outputs is expected to assure the following impacts:
- abatement of the nitrogen released in the collection systems from addressed industrial sources to less than 100 mg/l (end of the project: -2190 kgN/y; 5 years after the project: -330 t N/y)
- less than 25% oxygen required if compared to conventional full nitrification processes, and reduction of the N2O emitted during the biological process to less than 10% of current values (at the end of the project: -24.1 kgN2O/y ; 5 years after the project: -3.63 t N2O/y)
- reduction to less than a tenth of the sludge produced for nitrogen removal (at the end of the project: -3504 kg sludge(dry matter)/y; 5 years after the project: -528 t sludge(dry matter)/y)