Short communicationImpacts of monosodium glutamate industrial wastewater on plant growth and soil characteristics
Introduction
Monosodium glutamate or MSG was developed in Japan and has found extensive use as flavor enhancer in food products throughout South East Asia as well as in other countries. MSG was originally obtained by extraction from beet sugar and is presently produced by microbial fermentation of cassava, wheat, potato starch, etc. In this method, bacteria (strains of Micrococcus glutamicus) having the ability to excrete glutamic acid are grown aerobically in a liquid nutrient medium containing a carbon source (cassava, wheat, potato starch), a nitrogen source (ammonium ions or urea), mineral ions and growth factors. The glutamic acid is separated from the fermentation broth by filtration, concentration, acidification, and crystallization, followed by conversion to its monosodium salt. The entire process generates large amounts of wastewater effluents. The monosodium glutamate industrial wastewater (MSGW) contains high concentration of organic matter, COD, ammonium, sulphate and low pH (Yang et al., 2005) and hence biological wastewater treatments processes are not effective. Removal of nutrients and organics from the wastewater using algae (Gronlund et al., 2004) or aquatic plants (Upadhyay et al., 2007, Zimmels et al., 2008) are common bio-filtration techniques, and are not suitable for MSGW due to the high solid content and extreme pH. Incidents of direct disposal of MSGW into water-ways causing severe environmental problems were also reported recently (Overland, 2008). A few research studies have focused on partial treatments such as color and COD removal using different techniques (Yang et al., 2003, Jia et al., 2007).
Ecotechnology emphasizes reutilization of waste by suitable modifications. Nutrients present in organic-rich wastewaters and sludge are being reused as source of plant nutrition (Zurita et al., 2009). Consideration for the possible reuse of MSGW relies on the high levels of nutrients present in this wastewater. An earlier study pointed out that MSGW was phytotoxic as it inhibited the germination of tomato, wheat and Chinese cabbage seeds (Liu et al., 2007). But this conclusion was based on MSGW concentrations above 2%. On the contrary, Yang et al. (2005) described MSGW as a wastewater containing no harmful components and used as a raw material for single-cell protein production. Exploitation of this nutrient-rich organic wastewater in various applications needs to be studied to reduce the treatment costs and environmental pollution. We hypothesized that due to the presence of rich nutrients, at certain concentrations, the MSGW could show stimulatory effects on the plant growth. Hence, the objectives of this study were: (1) to characterize in detail the properties of MSGW, (2) to optimize the dose at which beneficial effects on plant growth can be observed by a seed germination assay and (3) to evaluate its effects on plant growth and some soil properties by a greenhouse pot experiment.
Section snippets
Wastewater collection and characterization
The MSGW samples were collected from Vedan Enterprise Corp., Taichung, Taiwan, in 25-l plastic containers and stored at 4 °C. Detailed characterization of the wastewater was carried out according to the standard methods for the analyses of water and wastewater (APHA, 1998). For the microbiological analyses, samples were separately collected in 20-ml sterile screw-capped glass tubes. Immediately after collection the samples were serially diluted and plated on nutrient agar and potato dextrose
Characteristics of the wastewater
MSGW was dark brown in color and highly turbid with high levels of total solids, N, organic C and very low pH (Table 1). The heavy metal contents were moderately low and within the permissible limits for land application (USEPA, 1989). The U.S. standards limit the heavy metal levels for agricultural application to 170 kg Zn ha−1, 78 kg Ni ha−1, and 46 kg Cu ha−1. Considering these qualities, the application rates for land use can be managed to avoid soil and groundwater contamination.
Effect of wastewater on seed germination
Germination index
Discussion and conclusion
This study shows that MSGW, an organic-rich wastewater enhanced the plant growth under moderate rates of application. Hence, it can be reused as a potential source for plant nutrients. Presence of pathogens such as fecal coliforms and Salmonella, is a common problem in the wastewaters from domestic, municipal and animal husbandry limiting direct utilization of such residues (Casteel et al., 2006). But overall microbial counts in the MSGW at the source of discharge were very low, without any
Acknowledgements
This research was supported by grants from the NSC, Taiwan, R.O.C. and Council of Agriculture, Executive Yuan, Taiwan, R.O.C. Singh S. is grateful for Taiwan Government scholarship.
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