Development of biofuels is considered as one of the important ways to replace conventional fossil energy and mitigate climate change. However, rapid increase of biofuel production could cause other environmental concerns in China such as water stress. This study is intended to evaluate the life-cycle water footprints (WF) of biofuels derived from several potential non-edible feedstocks including cassava, sweet sorghum, and Jatropha curcas in China. Different water footprint types including blue water, green water, and grey water are considered in this study. Based on the estimated WF, water deprivation impact and water stress degree on local water environment are further analyzed for different regions in China. On the basis of the feedstock resource availability, sweet sorghum, cassava, and Jatropha curcas seeds are considered as the likely feedstocks for biofuel production in China. The water footprint results show that the feedstock growth is the most water footprint intensive process, while the biofuel conversion and transportation contribute little to total water footprints. Water footprints vary significantly by region with climate and soil variations. The life-cycle water footprints of cassava ethanol, sweet sorghum ethanol, and Jatropha curcas seeds biodiesel were estimated to be 73.9–222.2, 115.9–210.4, and 64.7–182.3 L of water per MJ of biofuel, respectively. Grey water footprint dominates the life-cycle water footprint for each type of the biofuels. Development of biofuels without careful water resource management will exert significant impacts on local water resources. The water resource impacts vary significantly among regions. For example, based on blue and grey water consumption, Gansu province in China will suffer much higher water stress than other regions do due to limited available water resources and large amount of fertilizer use in that province. In term of blue water, Shandong province is shown with the most severe water stress issue, followed by Gansu province, which is attributed to the limited water resources in both provinces. By considering feedstock resource distribution, biofuel production potentials, and estimated water footprints, this study provides insight into the impact of biofuel production on the local water environment in China. Biofuel development policies need to be carefully designed for the sustainable development of biofuels in China.

We propose a novel dual-order backward-pumped distributed Raman amplification scheme assisted erbium-doped-fibre (EDF) providing nearly perfect signal power symmetry (>93% symmetry level) over two 50.4 km single mode fibre spans. Compared with conventional dual-order Raman schemes, this scheme only requires an additional short (25 cm) erbium-doped fibre to compensate the loss from the passive components between spans, significantly improving the overall link symmetry. Unlike a conventional hybrid Raman/EDFA approach with separate amplifier modules, the proposed scheme offers cost savings by utilizing the Raman pumps to activate the erbium-doped fibre, avoiding the need for an EDF-designated pump. In an optical transmission system with four 50.4 km fibre spans, our novel Raman scheme presented in this paper enables mid-link optical phase conjugation (OPC) to compensate up to 37 dB of nonlinear Kerr inter-signal interference. This represents a 12 dB advantage in compensation over conventional dual-order Raman amplification. Our experimental and simulated results also demonstrate that the proposed configuration provides 7 dB nonlinear threshold enhancement in a 200 Gb/s DP-16QAM 200 km inline transmission system using a mid-link OPC, exceeding the enhancement observed with the conventional dual-order Raman scheme. Our simulation results also show that the optimum Q2 factor using the proposed scheme outperforms the conventional schemes at 2000 km.

We propose and experimentally demonstrate a low-complexity pilot-assisted analytical method for polarization demultiplexing in SV-DD systems, achieving a 224-Gb/s 16QAM transmission over 40-km SSMF and can tolerate up to 75-krad/s RSOP at BTB.