Biological nitrate removal from synthetic wastewater using a fungal consortium in one stage bioreactors

Ha Greben,L-M Joubert,A Botha,He Whites,Mp Tjatji

doi:10.4314/wsa.v33i2.49094

Abstract

A series of lignocellulosic fungi, capable of cellulase and/or xylanase production, were isolated from soil to be used for cellulose degradation and nitrate removal from nitrate-rich wastewater in simple one-stage anaerobic bioreactors containing grass cuttings as source of cellulose. The fungal consortium, consisting of six hyphomycetous isolates, some of which belong to the genera Fusarium, Mucor and Penicillium, was able to remove a significant portion of the nitrate from the treated water.The results were obtained for three bioreactors, i.e. FR, FRp and AFRp, differing in volume and mode of grass addition. Bioreactor AFRp received autoclaved grass, instead of non-autoclaved grass containing natural microbial consortia, as supplied to FR and FRp. Nitrate removal in FR amounted to 89% removal efficiency, while this was 65% and 67% in FRp and AFRp, respectively. The residual chemical oxygen demand (COD) concentration in FR was higher than 600 mg/., while itwas 355 and 379 mg/. in FRp and AFRp, respectively. The similar nitrate removal results for AFRp and FRp indicated that the micro-organisms attached to grass cuttings did not seem to affect the nitrate removal in the reactor. This observation has led to the conclusion that the fungal consortium was, except for being able to degrade cellulose within the grass cuttings, also responsible for nitrate removal from the synthetic nitrate-rich wastewater

Highlights

Elevated nitrate (NO3-) concentrations in groundwater, ranging from 150 mg/l to 850 mg/l (NO3--N), are a threat to South African communities relying on groundwater as drinking water (Tredoux, 1993; Meyer et al, 1997; Tredoux et al, 2001)
Cellulose degradation using the fungal consortium showed that acetate (160 mg/l after 30 d) was produced from grass cuttings to which the fungal consortia had been added (Fig. 2)
A number of fungal species are well known for their ability to degrade grass cellulose, producing acetate (Lynd et al, 2002)

Summary

Introduction

Elevated nitrate (NO3-) concentrations in groundwater, ranging from 150 mg/l to 850 mg/l (NO3--N), are a threat to South African communities relying on groundwater as drinking water (Tredoux, 1993; Meyer et al, 1997; Tredoux et al, 2001). Simple- to-operate and cost-effective treatment technologies for nitrate removal from nitrate-contaminated groundwater should be investigated. Robertson and Cherry (1995) as well as Blowes et al (2000) demonstrated passive in situ nitrate removal methods that are mechanically simple and require little maintenance. Waste lignocellulose-containing solids, such as sawdust, grass cuttings and leaf compost, provided the carbon source for heterotrophic denitrification. Filamentous soil fungi of the genus Fusarium are known to utilise such waste materials as carbon source, and are known for their significant denitrification rates (Guest and Smith, 2002; Shoun et al, 1992). Since the first empirical evidence was obtained on fungal denitrification, numerous biochemical and molecular studies were conducted on this phenomenon, using pure cultures of various fungal taxa obtained from culture collections (Shoun and Tanimoto 1991; Shoun et al, 1992; Kobayashi et al, 1996; Shoun et al, 1998; Tsuruta et al, 1998; Zhou et al, 2002; Kumon et al, 2002; Watsuji et al, 2003)

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