Decontamination performance of a bioretention system using a simple sand-based filler proportioning method.

This study investigated the decontamination performance of a bioretention system using a sand-based filler constructed using sand and peat soil. The filler was constructed according to a simple proportioning method that considers water turnover time and organic content. Different inorganic constituents were added to the filler including zeolite, volcanic rock, coal slag, vermiculite and perlite to further improve the decontamination effect. Total suspended solids (TSS), total phosphorus (TP), ammonium nitrogen (NH4+-N), total nitrogen (TN) and chemical oxygen demand (COD) were measured in the influent and effluent. The results showed that: (1) the overall removal effect of the sand-based filler was satisfactory, indicating a certain feasibility and practicality of the method; (2) bioretention based on the sand-based filler had a better performance in removing TSS and TP with the removal rate both over 95%, and the addition of inorganic constituents to the filler was beneficial to TSS removal due to the effect of cumulative filtration capabilities of multiple materials, while phosphate was easily adsorbed by the positively charged particles of the peat soil; (3) the high removal rate of NH4+-N was due to adsorption and it could reach more than 80% by adding inorganic constituents with good adsorption such as zeolite vermiculite and perlite. Similarly, the addition of vermiculite and coal slag could increase the removal rate of COD by 15-25%. This research offers a novel alternative for guiding the selection and proportion of fillers in bioretention systems.

Liquefied dimethyl ether based multi-stage extraction for high efficient oil recovery from spent bleaching clay.

With the increasing production of spent bleaching clay (SBC), the recovery of the waste oil in SBC is becoming an important and urgent needs for our environment and economy. In this research, we have developed a new effective recovery technique to recover oil from SBC by use of liquefied dimethyl ether (DME). Over 65 wt% oil and 81% wt.% oil are efficiently recovered from SBC under equilibrium single-stage extraction conditions and multi-stage extraction conditions, respectively based on the systematically investigation to the effects of the DME/SBC ratio, extraction time, stirring speed and extraction stage number on oil recovery via a batch extractor. Compared with using other extraction solvents, the extraction solvent DME can be reused without heating and therefore significantly reduce the energy consumption during the oil recovery process. In addition, the quantitative oil extraction relationship is derived from the adsorption equilibrium model and is well verified by experimental results. The results show a great potential for using this oil recovery technique in SBC as well as in the large amount of oily sludge and oil sands.

An Experimental Study of Clogging Recovery Measures for Ceramic Permeable Bricks.

To explore the best clogging restoration measures for ceramic permeable bricks, ceramic permeable bricks were accurately clogged using a self-designed device by controlling the permeability, and different technical measures were adopted to restore the permeability. Then, the recovery effect, operating parameters and pore change inside the bricks using pressure washing were further discussed. The results showed that pressure washing was the best recovery measure, the joint methods was not recommended due to performance to price ratio. It was necessary to conduct pressure washing in relatively moist conditions, increase the cleaning frequency or prolong the cleaning time in the case of no serious blockage. Hydraulic cleaning can not only increase isolated pores but also remove the trapped solid particles, and increase the proportion of connected pores and dredges through water channels. This research offers some reference for the daily maintenance of permeable bricks.

Risk of contamination of infiltrated water and underground soil by heavy metals within a ceramic permeable brick paving system.

The risk of heavy metal contamination of infiltrated water and underground soil on a permeable brick paving system was investigated. The paving system was constructed as a frame structure base on top of a 1.0-m-thick clay layer with permeable ceramic brick at the surface. The concentrations of heavy metals (Zn, Cu, and Pb) in infiltrated water and soil at different underground depths under the paving system were measured. Speciation rates of Zn, Cu, and Pb at different clay depths were further determined to ascertain the probability of downward migration of the unstable forms. The results showed reduced risk of infiltrated water pollution by heavy metals due to underground soil acting as an effective trap. However, topsoil was more susceptible to heavy metal pollution, with the different pollution soil depths of Cu, Zn, and Pb mainly attributed to the different binding abilities between the heavy metals and soil. Soil Cu and Zn remained relatively stable, whereas there was a potentially high risk of Pb migration. The study found that topsoil could accumulate non-degradable heavy metals to unacceptable levels over a period of 30 years and that topsoil should therefore be replaced after 30 years to reduce the risk of soil pollution. This study fills a knowledge gap by both determining the risks of heavy metal pollution to underground soil and infiltrated water and exploring effective ways to reduce heavy metal pollution.

Influence of fillers on the removal of rainwater runoff pollutants by a permeable brick system with a frame structure base.

To fully investigate the effectiveness of fillers in the removal of pollutants from rainwater, gravel, zeolite, slag, volcanic rock and iron filings with a 3-5 cm particle size were applied to construct a brick paving system with a frame structure for the removal of pollutants. Total suspended solids (TSS), chemical oxygen demand (COD), ammonia nitrogen (NH3-N), total nitrogen (TN), total phosphorus (TP) and heavy metals (Cu, Zn, and Pb) in the influent and effluent were measured, and the effectiveness and mechanism of pollutant removal were further investigated. The results showed that the permeable brick system effectively reduced TSS, TP, Zn, Cu and Pb and was relatively ineffective in reducing NH3-N, TN and COD. The removal results obtained using different materials show that (1) physical interception is the main reason for TSS and TP removal, (2) the adsorption and ion exchange properties of zeolite enable it to highly absorb ammonia nitrogen, (3) iron filings can effectively reduce NO3-N, and (4) adding fillers rich in iron oxide, such as volcanic rock or slag, can contribute to COD adsorption. The study provides a feasible technical path for improving the practicability of permeable pavement.