Evaluation of struvite obtained from semiconductor wastewater as a fertilizer in cultivating Chinese cabbage
Highlights
► Recovered struvite from semiconductor wastewater was evaluated as fertilizer. ► The struvite showed more outstanding fertilizing effects than commercial fertilizers. ► Cu, Cd, As, Pb and Ni were observed at very low level in the vegetable tissue. ► The optimum struvite dosage for the cultivation of Chinese cabbage was 1.6 g struvite/kg soil.
Introduction
Semiconductor wastewater generally contains the high levels of ammonium (NH4) and phosphate (PO4). It is well known from the previous studies that struvite precipitation is very effective in the removal of ammonium and phosphate of semiconductor wastewater. In field-scale study, Ryu et al. [1] showed that struvite precipitation brought about a high NH4–N removal efficiency of over 89% on average. Also, it was reported that NH4–N removal can be enhanced up to 98% by increasing mixing speed in lab-scale study [2]. Moreover, the study of Warmadewanthi and Liu [3] revealed that the removal and recovery of PO4–P and NH4–N from semiconductor wastewater as struvite is feasible. Some studies also presented that struvite precipitation by the dissolved CO2 degasification technique resulted in the effective removal of NH4–N and PO4–P [4], [5].
However, a considerable amount of struvite produced as a by-product during the removal of ammonium and phosphate has caused another problem of waste disposal. A feasible solution to the problem would be its reuse as a fertilizer because struvite is composed of magnesium (Mg), ammonium and phosphate in equal molar concentrations. The previous study showed that struvite was preferred as a good fertilizer in agriculture for its slow-release rate and much lower impurity [6]. Especially, the presence of Mg in struvite makes it more attractive as an alternative to contemporary fertilizers for a few crops, like sugar beets, that require magnesium [7]. Moreover, since struvite is slightly soluble in water and soil solutions, slow-release struvite has been found to be a highly effective source of phosphorus, nitrogen and magnesium for plants through both foliar and soil application.
Although struvite has been qualified as a fertilizer, as mentioned above, to the best of our knowledge, the plant availability and fertilizer value of struvite precipitate obtained from semiconductor wastewater was never tested before. Such reason for lack of study may be attributable to the fact that semiconductor wastewater commonly contains many refractory chemicals such as organic solvents, acids, bases, salts, heavy metals, fine suspended oxide particles and other organic and inorganic compounds [8], [9].
The present study was therefore aimed at investigating the feasibility of the plant availability of nutrients recovered from semiconductor wastewater by struvite precipitation. Specifically, objectives of this study were: (1) to characterize precipitated struvite obtained from a real semiconductor wastewater treatment plant; (2) to evaluate the fertilizing value of struvite precipitate with pot trial tests for cultivation of Chinese cabbage by comparing it with commercial fertilizers; (3) to determine the optimum dosage of struvite precipitate for cultivation; and (4) to analyze the levels of nutrients and heavy metals in vegetables tissue grown with struvite and other fertilizers.
Section snippets
Collection of struvite
The struvite deposit for experiments were obtained from a semiconductor wastewater treatment facility (SWTF) located in Cheongju, Republic of Korea, where struvite precipitation has been employed to remove ammonia nitrogen (NH4–N) and orthophosphate (PO4–P) from wastewater as illustrated in Fig. 1. The SWTF handled a quantity of 500 m3 of wastewater per day. Table 1 shows the composition of semiconductor wastewater treated in that facility. The wastewater contained significantly high
Characteristics of struvite deposit
To determine the morphology, the obtained precipitated matters were examined by SEM and the SEM micrograph is illustrated in Fig. 2. The crystal size of struvite deposit was widely distributed in the range 100 μm.
XRD analysis was also used to characterize the purity of struvite deposits collected from SWTF. The X-ray diffractograms exhibited several peaks indicative of the struvite presence as illustrated in Fig. 3. The XRD pattern generated from the precipitated matters matched with the
Conclusions
Struvite recovered from semiconductor wastewater was applied in cultivation of Chinese cabbage. The fertilizing value of struvite was evaluated by comparing it with commercial fertilizers by pot trial tests. Furthermore, the optimum struvite dosage was determined. Based on the experimental results, the following conclusions were drawn:
- (1)
The capability of struvite as a fertilizer far surpassed other fertilizers except for complex fertilizer during the experimental period of 32 days. Also, it was
Acknowledgment
This research was supported by Ministry of Environment as “The Eco-Innovation Project of 2011”, Republic of Korea.
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