Advanced Water Management Centre

Iron salt use in urban water systems (MULFE)

Thursday, 19 March 2020
  • Image of two workers taking samples at a treatment plant

The MulFe project developed an integrated and innovative strategy to substantially reduce chemical use in urban water management, delivering large economic and environmental benefits to water utilities. The strategy generates multiple benefits from iron salts (Fe) by repurposing iron three to four times within the urban water system.

The first phase of the project assessed the effect of in-sewer dosing of iron salts on the downstream wastewater treatment and bioenergy recovery processes. Laboratory testing was combined with full-scale field testing. Two unique laboratory-scale systems were constructed, each comprising two sewer reactors, a sequencing batch reactor for biological wastewater treatment, a sludge thickener, and an anaerobic sludge digester. This is likely the first laboratory system worldwide to simulate an entire, integrated urban wastewater system. Two full-scale field trials dosing Fe were conducted in close collaboration with Urban Utilities.

Results from the laboratory-scale urban water system showed that in-sewer dosing of 10 mgFe L-1 FeCl3 decreased the dissolved sulfide concentration in sewer effluent by ~4.3 mgS L-1 (1st use), and decreased wastewater phosphorus concentration in downstream wastewater treatment by ~4.7  mgP L-1 (2nd use), but did not interfere with key biological processes such as nitrogen, COD and solids removal. In-sewer dosing of FeCl3 also decreased H2S concentration in biogas (3rd use) but did not affect biogas production performance. The dewaterability of anaerobically digested sludge was improved by 18% with in-sewer dosing of FeCl3, and the settleability of activated sludge in the bioreactor was also significantly improved.

In full-scale field trials of FeCl2 dosing in two wastewater catchments, results were consistent with those obtained in laboratory studies, and also consistent across catchments. Implementing the Mulfe strategy amounted to combined savings of approximately $1.5m pa for the two catchments.

The second phase of the project employed laboratory and pilot studies to assess the effects of in-sewer dosing of iron-rich drinking water sludge on sewers and on the downstream wastewater treatment systems. This strategy uses iron chloride to replace alum, a commonly used coagulant, for drinking water treatment (1st use). The iron-rich drinking water sludge thus produced is then repurposed for sewer dosing. The laboratory studies showed that iron in the drinking water sludge is as effective as iron salts in sulfide control in sewers (2nd use), phosphate removal from wastewater (3rd use) and hydrogen sulfide removal in biogas (4th use). The dewaterability of anaerobically digested sludge was also improved to a similar extent. Experiments carried out on two pilot-scale rising main sewers at the Urban Utilities Innovation Centre confirmed the availability of iron in drinking water sludge for in-sewer sulfide removal.

In summary, the MulFe project identified clear opportunities for water and wastewater utilities to collaborate and share the benefits, providing services at reduced costs with improved environmental sustainability. The MulFe project was recently awarded the 2019 Australian Water Association Research Innovation Award (Queensland) and is a finalist in the national award round, to be announced at OzWater’20 in Adelaide, May 2020.

MULFE team at AWA Awards night.

ARC Linkage Project LP140100386 An integrated approach to iron salt use in urban water systems (MulFe) was created, funded and delivered in strong collaboration between The University of Queensland, Urban Utilities, Seqwater, Water Research Australia Ltd, District of Columbia Water and Sewer Authority, Public Utilities Board of Singapore, and Catalan Institute for Water Research. The project commenced in 2015, ran for 4 years, and supported 4 full-time postgraduate students based at UQ.