河流底泥活性覆盖板的制备及其对城市内河底泥氮磷释放的抑制效果

Preparation of active capping plate for sediment in urban river and its effect on nitrogen and phosphorus reduction

我国部分城市内河氮磷严重超标,成为水体富营养化的诱因之一,故需采取消减措施。底泥覆盖法可有效削减城市内河氮磷,但颗粒状覆盖材料具有施工时不易均匀覆盖、雨季行洪排涝时又易流失等问题,从而导致氮磷效果不理想。因此,本研究尝试采用活性覆盖板来控制底泥氮磷释放。活性覆盖板由铝基锁磷剂、水泥和粉煤灰作为主要原料制备而成。考察了材料配比、水料比、成型压力和铝基锁磷剂颗粒粒径等4个因素对活性覆盖板的抗冲刷性能和透水性能的影响;通过室内静态模拟实验探究了活性覆盖板覆盖对氮磷释放的控制效果。结果表明,活性覆盖板制备最佳工况条件为铝基锁磷剂(粒径1~3 mm)、水泥和粉煤灰占比分别为70%、15%和15%;水料比为0.25;成型压力为1.00 MPa;活性覆盖板具很好的抗冲刷性能和透水性能,其抗冲刷系数和透水系数分别为98.01%和0.139 cm·s^(-1);活性覆盖板主要含有Si、Al、Ca和Fe等元素,其质量分数分别为28.99%、26.99%、22.78%和14.50%;与对照系统相比,活性覆盖板系统对底泥TP和NH_(4)^(+)-N释放的平均削减率分别为73.78%和53.93%;覆盖系统上覆水氮和磷质量浓度与对照系统均存在显著差异(P<0.05),由此可见,活性覆盖板能够有效控制污染河流底泥氮磷释放。

Nowadays,the overloaded nitrogen and phosphorus in some Chinese urban rivers was deemed one of the factors that induces water eutrophication.Thereby,it is necessary to take actions for eutrophication abatement.The in-situ capping method is an effective treatment method to reduce nitrogen and phosphorus in urban inner rivers.However,the granular capping material has problems such as not easy to be uniformly distributed during construction,and easy to lose during flooding and drainage in the rainy season,which leads to the deterioration of the reduction effect of nitrogen and phosphorus.Aiming at these problems,the active capping plates were seminally employed to reduce the nitrogen and phosphorus from contaminated sediment.In brief,this active capping plate was prepared from Al-PIA,cement and fly ash as the main raw materials.The effects of material ratio,water/material ratio,forming pressure and Al-PIA particle size on the scour resistance and water permeability were subsequently examined.In addition,the indoor static simulation test was conducted to investigate the performance of active capping plate on controlling the release of phosphorus and nitrogen by taking the contaminated sediment as the probe.The results revealed that the optimum working conditions for active capping plate preparation were following:the proportion of 70%,15% and 15% for Al-PIA(particle size ranges from of 1~3 mm)cement or fly ash,respectively,the water/material ratio of 0.25,and forming pressure of 1.00 MPa.Under these conditions,the prepared active capping plate had good scour resistance and water permeability with scour resistance coefficient of 98.01%and water permeability coefficient of 0.139 cm·s^(-1).The active capping plate mainly contained elements such as Si,Al,Ca,Fe,and their mass fractions were 28.99%,26.99%,22.78%,14.50%,respectively.Moreover,in comparison with the control system,the average reduction rates of TP and NH_(4)^(+)-N releasing from contaminated sediment by active capping plate system were 73.78% and 53.93%,respectively.The phosphorus and nitrogen concentrations in the overlying water of capping system significantly differed from those of the control system(P<0.05),indicating the active capping plate was effective in controlling the release of nitrogen and phosphorus from the contaminated sediment.