Summary of study conducted by University of Innsbruck:

Title:
Possible weight reduction and hygienic benefits through the
ventilated bioMat ® Combi-system and Mater-Bi BioBags?

Questions concerning the hygienic aspects of waste bins and buckets for food waste collection in households have arisen since the collection of source separated waste became widespread. The choice of an appropriate food waste collection system and more frequent emptying of the food waste might prevent many of the negative side-effects like bad odors and the increased occurrence of moulds.

For this investigation, three different household food waste collection systems (Fig. 1) were tested regarding optical quality and odor emission, number of airborne fungi and weight loss of the food waste. Compostable BioBags, made from the biodegradable starch based material Mater-Bi were used for the ventilated "Combi" BioBag holder system (BS-COM) and one system using BioBags in closed kitchen bins (BS-BK), the third version was made up of polyethylene-bags in closed kitchen bins (PE-BK).

Fig. 1
Household food waste collection systems under investigation: BS-COM, BS-BK and PEBK (from the left).

Bio-waste, consisting mainly of food waste, was collected at a nearby housing estate and distributed to 15 replicas of each version.

After three, seven and 14 days the weight loss of each system, optical appearance and number of colony forming units (cfu) on malt-extract-agar and dichloran-glycerin-agar plates that had been attached to the lids of the containers, were analyzed.

After three days of storage a mean weight loss of 15% could be found in the BS-COM-systems.

After 7 days the mean weight loss of the biowaste in the ventilated "Combi" system (BS-COM containers) was 32%, compared to 3.7% and 3.8% for the closed kitchen bins (BS-BK and PE-BK, respectively) (Fig. 2).

Weight loss was significantly correlated with cfu for the Combi (BS-COM) systems (p<0.01). Mean numbers of airborne fungi were lower for the ventilated "Combi" system (BS-COM) at all three days of investigation. Significantly lower cfu could be found after one week (p<0.01), whereas numbers for the closed bins with PE liners (PE-BK) increased (Fig. 3).

Very high numbers of maggots found mainly in the closed kitchen bins with PE liners (PE-BK) and strong growth of moulds vitiated the optical quality of both closed kitchen bin variants (Tab. 1).

Fig. 2
Weight loss in % for BS-COM, BS-BK and PE-BK (n = 15 ± mean) after 3, 7 and 14 days.

Fig. 3
Number of colony forming units (cfu) on malt-extract agar (left) and DG18-agar-plates (right), placed on the inside of the lids of the variants BS-COM (n = 6 ± mean), BS-BK (n = 6 ± mean) and PE-BK (n = 12 ± mean) after 3, 7 and 14 days

Leaking fluids (leachate) that accumulated at the bottom of the kitchen bins led to very bad odours after 14 days of incubation.

Most of the biobags in the closed kitchen bins became weakened and could not be removed as a whole.

With the ventilated "Combi" system (BS-COM) no water leakage and no increase in bad odours could be found even at day 14. The open construction of the "Combi" BioBag holder has enhanced water evaporation through the permeable starch based biobags but prohibited leakage. The BioBags maintained their stability in the ventilated "Combi" system (BS-COM) and could be easily removed and disposed.

Tab. 1
Examples of the differences in optical quality of biowaste collected in BS-COM, BS-BK and PE-BK after 3, 7 and 14 days.