Qing Tao Zhang

Effects of Evapotranspiration on Mitigation of Urban Temperature by Vegetation and Urban Agriculture

The temperature difference between an urban space and surrounding non-urban space is called the urban heat island effect (UHI). Global terrestrial evapotranspiration (ET) can consume 1.4803×1023 joules (J) of energy annually, which is about 21.74% of the total available solar energy at the top of atmosphere, whereas annual human energy use is 4.935×1020 J, about 0.33% of annual ET energy consumption. Vegetation ET has great potential to reduce urban and global temperatures. Our literature review suggests that vegetation and urban agricultural ET can reduce urban temperatures by 0.5 to 4.0°C. Green roofs (including urban agriculture) and water bodies have also been shown to be effective ways of reducing urban temperatures. The cooling effects on the ambient temperature and the roof surface temperature can be 0.24-4.0°C and 0.8-60.0°C, respectively. The temperature of a water body (including urban aquaculture) can be lower than the temperature of the surrounding built environment by between 2 and 6°C, and a water body with a 16 m2 surface area can cool up to 2 826 m3 of nearby space by 1°C. Based on these findings, it can be concluded that the increase of evapotranspiration in cities, derived from vegetation, urban agriculture, and water body, can effectively mitigate the effect of urban heat islands.

Potential energy production from algae on marginal land in China.

This study is aimed to systematically estimate marginal land resources with different grades (total area; land with certain eco-environmental-economic feasibility; centralized reserve land) in China, and evaluate potential energy production from microalgae on marginal lands in the long-, mid- and near-term, based on a model. The annual potential energy production from algae in total marginal land of China (APEMC) was estimated to 4.19 billion standard coal equivalent (tce), far more than total annual energy consumption equivalent in China (TECCE) in 2007. For microalgae with 35% lipid content, the APEMC in the mid-term would be 37.6-65.8% of the TECCE in 2007. The corresponding annual CO(2) emission mitigation by replacement of fossil fuels by algal bioenergy would be 4.27-7.44 billiont. Although Southwest China provides the highest potential algae production in the long-term, Northwest China provides the highest value in the near-term.

Technologies for Efficient Use of Irrigation Water and Energy in China

Abstract While the shortage of water and energy is a well-recognized worldwide natural resources issue, little attention has been given to irrigation energy efficiency. In this paper, we examine the potential energy savings that can be achieved by implementing improved irrigation technologies in China. The use of improved irrigation management measures such as a flow meter, irrigation scheduling, and/or regular maintenance and upgrades, typically reduces the amount of water pumped over the course of a growing season. The total energy saved by applying these improved measures could reach 20%, as compared with traditional irrigation methods. Two methods of irrigation water conveyance by traditional earth canal and low pressure pipeline irrigation (LPPI) were also evaluated. Our study indicated that LPPI could save 6.48×109 kWh yr−1 when applied to 11 Chinese provinces. Also, the CO2 emission was reduced by 6.72 metric tons per year. Among these 11 surveyed provinces, the energy saving potential for two provinces, Hebei and Shandong, could reach 1.45×109 kWh yr−1. Using LPPI, potential energy saved and CO2 emissions reduced in the other 20 Chinese provinces were estimated at about 2.97×109 kWh yr−1 and 2.69 metric tons per year, respectively. The energy saving potential for Heilongjiang, a major agriculture province, could reach 1.77×109 kWh yr−1, which is the largest in all provinces. If LPPI is applied to the entire country, average annual energy saving of more than 9 billion kWh and average annual CO2 emission reduction of more than 9.0 metric tons could be realized. Rice is one of the largest users of the worlds fresh water resources. Compared with continuous flooding irrigation, intermittent irrigation (ITI) can improve yield and water-use efficiency in paddy fields. The total increments of net output energy and yield by ITI in paddy fields across China could reach 2.5×1016 calories and 107 tons, respectively. So far only a small part of agricultural land in China has adopted water and energy saving technologies. Therefore, potential water and energy savings in China by adapting improved irrigation technology could be significant and should be carefully studied and applied.

The Growth Performance of Duckweed and Removal Rate of Nitrate and Phosphorus in Sewages with Different Processes

The growth performance of duckweed (Spirodela polyrrhiza) and its removal rate of nitrate and phosphorus in sewages taken from sewage treatment plant with different processes were studied. The experiments were conducted in an environmentally controlled growth chamber. Three kinds of sewages were taken from a grit chamber, a sedimentation tank, and the anoxic pond in a sewage treatment plant, respectively. The fourth kind of sewage was mixed using the sedimentation tank sewage and the anoxic pond sewage in a volumetric ratio 1:1. The weight of duckweed biomass were determined with a balance. Wastewater samples taken from the media were analyzed for total nitrogen (TN), ammonium nitrogen (NH4N), total phosphorus (TP), phosphatephosphorus (PO4P) using AA3 Continous Flow Analyzer. The results showed that Spirodela polyrrhiza grew well in sewages taken from grit chamber and sedimentation tank of a sewage treatment plant, whereas a lot of duckweed fronds were dead in the sewage taken from the anoxic pond due to the high TP (higher than 7.9 mg/L) and TN (higher than 51.6 mg/L). The suitable TN concentration for Spirodela polyrrhiza growth should not be higher than 45 mg/L. Compared with the treatments without duckweed, the NH4N concentrations were reduced more than 60% in ST and GC sewages with duckweed due to the NH4N uptake by duckweed. Spirodela polyrrhiza could remove TN efficiently in sewages with relative low concentration TN (less than 20 mg/L), while duckweed could not remove TN effectively in sewages with high concentration TN (higher than 20 mg/L). The TN concentration in GC sewage decreased greatly in the first four days, which probably brought about anaerobic condition, thus P uptake switched to net release of P, which caused the increase of the TP concentration in the GC sewage without duckweed in the last six days. O2 or oxidant should be provided for sewage treatment system using duckweed to ensure that efficient removal of TN and TP meanwhile. The TP and PO4P concentrations in the mixed sewage with duckweed increased far more than those for no-duckweed treatments, which could be related that the dead duckweed released P into the sewage.