Venice, Italy

Applied technologies

Ammonium sulphate production (air stripping & scrubbing)

Biogas production via anaerobic digestion

Reverse Osmosis

Ultrafiltration or nanofiltration with RO regenerated membranes

Key performance indicators

Industrial reuse of water: at the moment the quantity of treated wastewater supplied to industries in the area of ​​Porto Marghera represents only 4% of the total freshwater supplied. As the tests have demonstrated the high quality and stability of the recovered water, the quality concerns have been overcame and the target for effluent reuse can easely increase. 

Ammonia recovery: within the regional water service, the performance showed by the tests with the pilot plants allows to identify a total regional potential of Nitrogen recovery of about 500 t N/y, which corresponds to less 1% of the mineral Nitrogen applyed at regional level but implies a saving of CO2 equivalent of approximately 6,000 t/y. 

Synergistic benefits

Ammonia recovery: the anaerobic digestion treatment of LOWs is in clear synergy with the recovery of ammonium fertilizer for the increase of both the quantity of recoverable ammonia nitrogen and the potential energy saving. Moreover, the synergic application of stripping and LOW-sludge codigestion at regional level can led to an annual saving of carbon footprint of about 14,000 t CO2 eq. 

T.his results are in synergy with the results provided by the IT tool dedicated to sludge, that allow to outline the total Nitrogen potential recovery linked to the total agricultural sludge valorizatiion.

Requirements and conditions

Stripping technologies:

• CS has proven to be relatively sensitive to the presence of solids and alkalinity; the centrates normally produced by anaerobic digestion of sludge are not a problem (up to 1,500 mg TSS/l and 2,500 mg CaCO3/l) but heavier wastewaters should be well assessed because they may become impossible to treat with this technology, despite pretreatment;
• AS is particularly suitable in the presence of very concentrated wastewater (e.g. 12,500 mg TSS/l and 20,000 mg CaCO3/l) and waste heat availability but may become unsustainable if it is necessary to achieve high ammonia nitrogen removal yields (e.g. 80%).

Key lessons

Industrial reuse of water: ultrafiltration and reverse osmosis were sufficient to ensure the required quality, while the addition of electrodeionization allowed slight improvements only for a few parameters, resulting superfluous in the context of the Venice LL.

Ammonia recovery: The results of both technologies demonstrated the existence of promising application areas in ammonia recovery in WWTP concentrated streams. The interest in this application derives both from the possibility of obtaining marketable ammonium salts and from the reduction of energy consumption and carbon footprint as a consequence of the cut in N2O production in WWTPs and the replacement of ammonia produced with the Haber-Bosch process.

CS technology has proven to be suitable where solids and alkalinity can be removed by pretreatment, using reagents and producing sludge. AS is preferable for wastewater containing very high concentrations of solids and alkalinity; it does not use reagents and does not produce sludge but requires somewhat larger spaces and more thermal energy.

The co-digestion of concentrated LOW and waste activated sludge significantly increased biogas production compared to sludge digestion alone, resulting in a promising approach to increase the potential energy self-sufficiency of WWTPs.

IT tools on water reuse and sludge valorization: the development of these tools had to deal with important problems related to the availability of basic data, with particular reference to the absence of some of them, the fragmentation of sources, the updateability and the inhomogeneity with which they are expressed individually and structured in the source databases. All this required intense research and dialogue with the sources and pre-treatment, verification and cleaning of the information.

A further commitment was necessary to guarantee the standardization of the tools, their interoperability and applicability in contexts other than the one for which they were created.

Legislation and policy recommendations

Below are the main applicable rules

Pilot - industrial reuse of water:

• Italian DM 185/03

Pilot - ammonia recovery:

• Regulation (EU) 2019/1009
• Italian DLgs 1152/06
• Italian DLgs 75/10

IT tool - water reuse:

• Regulation (EU) 2020/741
• Italian DM 185/03
• Italian DL 39/23

IT tool - sludge valorization:

• Italian DLgs 99/92
• Regional DGR Veneto 2241/05 (currently under revision)

• 2000/60/EC EU Water Framework Directive