Interrogating the effect of decentralized biogas injection on a natural gas network

Biogas from renewable sources and natural gas(NG) are both high-efficient and good-quality gaseous fuels on account of their enrichment in methane. Due to the dissimilar physical properties of biogas and NG, biogas cannot substitute NG directly without treatment and is usually used on site due to the high cost of the transportation and distribution via exclusive pipeline system. Consequently, the injection of biogas into existing NG infrastructure was proposed to address the deficiency. In this paper, the Wobbe index (WI) as well as the combustion potential (CP) were introduced for analyzing the interchangeability of an NGbiogas mixture, and a mathematical framework was put forward for modeling and simulating NG grid with a decentralized biogas injection. Results show that the maximum admissible amount of biogas in mixture was 10.5% by volume. A medium pressure network was used to interrogate the comprehensive effect of distributed biogas injection, which showed an impact on both gas quality and hydraulic regime across the grid.

Aquaculture Solids Management Using A Combination of Sand/Gravel or Unwoven Fabric Bed With Lolium perenne Lam as A Plant Biofilter

Objective This work is an evaluation of the efficiency of a sand-gravel or unwoven fabric bed system and Lolium perenne Lam as plant biofilter in the reduction of solids and nutrients removal from aquaculture discharge water. Methods The fzrst step consisted of the collection of wastewater in the tank and the distribution at three different hydraulic loading regimes （0.5, 1, 1.5 L/hour） to the different experimental systems. The second step was to evaluate the performance of the different systems. The fzrst system consisted of a bucket filled with a substrate of sand/gravel （20 cm in depth）, on the bottom of which was a 80 mesh/inch2 of nylon （S1）; the second was similar, but was planted with Lolium perenne lam （S2）; the third was planted with a grass plate consisting of 7 layers of unwoven fabric planted with L. perenne （S3）. Results The second system showed the best performance in reducing solids as well as in nutrients （TN, TP, and COD） reduction. The removal rates for TS, TN, and TP were negatively correlated with the loading regimes, with 0.5 L/hour being the most efficient and thus taken as the reference. Conclusions Solids management using a sand/gravel substrate as bed culture and Lolium perenne L. as plant biofilter has proved to be an efficient technique for solids reduction with low operating cost. This grass plays an important role in wastewater eco-treatment by absorbing dissolved pollutants （TAN） as nutrients for its growth.

Flow regime and head loss in a drip emitter equipped with a labyrinth channel

Labyrinth channels are widely adopted in emitter designs to regulate the water flow.The flow regime and the head loss of labyrinth channels have significant impacts on the hydraulic performance of emitters.In this study,the flow behavior of water passing through an emitter channel is observed using the micro particle image velocimetry（PIV）,and the head loss during the flow is analyzed for an emitter with a triangular labyrinth channel.The results show that the flow regime is consistent with the classical theory of hydraulics governing straight channels,even when the cross-sectional area is very small（as small as 0.5 mm×0.5 mm）.The critical Reynolds number from laminar to turbulent flows in a labyrinth channel is approximately in a range between 43 and 94.The local head loss factor decreases as the Reynolds number increases for labyrinth channels with smaller cross-sectional areas,such as 0.5 mm×0.5 mm and 1.0 mm×1.0 mm.The local head loss factor is not related to the Reynolds number and is only a function of the boundary conditions of the labyrinth channel when the Reynolds number exceeds approximately 1 000（for cross-sectional areas of 1.5 mm×1.5 mm and 2.0 mm×2.0 mm）.The ratio of the local head loss to the total head loss total（ /）j fh h first increases and then remains nearly constant as the Reynolds number increases in the labyrinth channel.The head loss in the labyrinth channel is almost equal to the local head loss,and total（ h_j/h_（ftctal））is approximately 0.95 for cross-sectional areas of greater than 1.0 mm×1.0 mm.These results can be used for optimizing the design of emitter channels.