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Sensors 2016, 16(2), 244; doi:10.3390/s16020244

Determination and Visualization of pH Values in Anaerobic Digestion of Water Hyacinth and Rice Straw Mixtures Using Hyperspectral Imaging with Wavelet Transform Denoising and Variable Selection

1
College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China
2
School of Information Engineering, Zhejiang A&F University, Hangzhou 311300, China
*
Authors to whom correspondence should be addressed.
Academic Editor: Ki-Hyun Kim
Received: 2 December 2015 / Revised: 11 February 2016 / Accepted: 14 February 2016 / Published: 18 February 2016
(This article belongs to the Special Issue The Use of New and/or Improved Materials for Sensing Applications)
View Full-Text   |   Download PDF [1269 KB, uploaded 18 February 2016]   |  

Abstract

Biomass energy represents a huge supplement for meeting current energy demands. A hyperspectral imaging system covering the spectral range of 874–1734 nm was used to determine the pH value of anaerobic digestion liquid produced by water hyacinth and rice straw mixtures used for methane production. Wavelet transform (WT) was used to reduce noises of the spectral data. Successive projections algorithm (SPA), random frog (RF) and variable importance in projection (VIP) were used to select 8, 15 and 20 optimal wavelengths for the pH value prediction, respectively. Partial least squares (PLS) and a back propagation neural network (BPNN) were used to build the calibration models on the full spectra and the optimal wavelengths. As a result, BPNN models performed better than the corresponding PLS models, and SPA-BPNN model gave the best performance with a correlation coefficient of prediction (rp) of 0.911 and root mean square error of prediction (RMSEP) of 0.0516. The results indicated the feasibility of using hyperspectral imaging to determine pH values during anaerobic digestion. Furthermore, a distribution map of the pH values was achieved by applying the SPA-BPNN model. The results in this study would help to develop an on-line monitoring system for biomass energy producing process by hyperspectral imaging. View Full-Text
Keywords: hyperspectral imaging; anaerobic digestion; pH value; distribution map; variable selection hyperspectral imaging; anaerobic digestion; pH value; distribution map; variable selection
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Zhang, C.; Ye, H.; Liu, F.; He, Y.; Kong, W.; Sheng, K. Determination and Visualization of pH Values in Anaerobic Digestion of Water Hyacinth and Rice Straw Mixtures Using Hyperspectral Imaging with Wavelet Transform Denoising and Variable Selection. Sensors 2016, 16, 244.

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