Metal concentrations should not exceed the allowable standards,
and they should be monitored before digestion [28]. Toxic
substances such as cadmium, lead and phosphorus can inhibit
methane formation and reduce its efficiency. Selected elements,
including calcium, potassium, magnesium, iron, zinc, manganese,
copper and cobalt, speed up digestion, but their concentrations
cannot exceed the applicable standards [29]. Inhibitors can be
precipitated, neutralized and diluted. Other microelements can be
added to neutralize the adverse effects of inhibitors [30]. The above
processes were described by Talarowska et al. [31] who analyzed
carbon and metal concentrations in food wastes for biogas production
(methane formation). Other studies have demonstrated
that although methane-producing bacteria are deactivated by
toxins, they can survive for long periods of time in an unsupportive
environment, which does not affect their ability to biodegrade
organic compounds [32].
Feedstock preparation often involves maceration and the formation
of a suspension. A suspension is separated by hydrocyclone
fractionation, screening or floatation. Organic components are also
separated from metals and other undesirable substances by gravity
separation [33]. Toxic compounds inwastes that are used as organic
fertilizers can be assimilated by plants and accumulated in harmful
concentrations [34] and[35]. Toxin levels in soil andfertilizers should
be determined in viewof the strong correlations between metal ions
and organic compounds [36], nutrient concentrations in the substrate
[37] as well as the influence of synergistic and antagonistic
relationships between ions on the toxicity of minerals [38]. The
above problems have also been investigated by Jasiewicz et al. [39].
The objective of this study was to determine the concentrations
of heavy and light metal cations in food wastes and their influence
on the analyzed substrates' suitability for biogas production.