The biofilms were supported on suspended carriers made
of light polymeric materials. The bench-scale system was
running parallel to the existing biotreatment plant. Principal
parameters for assessing treatment performance include
chemical oxygen demand (COD), biochemical oxygen demand
(BOD), nitrogen, phosphorus, and total suspended
solids (TSS). The bench-scale experiment was operated for
six months during 2003-2004. Major results include the
following. (i) BOD5 was reduced from 238 to only 7.7 mg/L,
well below the discharge standard and treatment target of
30 mg/L. The overall BOD removal efficiency was a very
impressive 96.7%. In comparison, the BOD5 from the existing
biotreatment was 56.9 mg/L, with only 76% removal. (ii) COD
removal was 85%. However, the effluent COD from the ZVIbio
system was 73 mg/L, suggesting that a large fraction of
the organic substance in the effluent was still nonbiodegradable.
(iii) The removal efficiency for total nitrogen
increased from 38% to 51.2% while ammonia removal
improved from 13.3% to 92%. (iv) The observed effect on the
color removal was significant, with over 75% reduction in
the color transmittance measurements. (v) Total phosphorus
in the effluent was reduced from 2.3 to 1.5 mg/L.
Additional results from the laboratory experiments can
be found in the Supporting Information (Table S2a). The
bench-scale experiment demonstrates the promising potential
of the ZVI pretreatment for enhanced biological
treatment of mixed industrial wastes. The bimetallic structures
form nano- and microscale galvanic cells with the
metallic iron as the electron donor for the reduction and
partial degradation of organic compounds. The reaction
products from the ZVI reactor are apparently more biodegradable
by aerobic microorganisms.