Nitrogen evolution during the co-combustion of hydrothermally treated municipal solid waste and coal in a bubbling fluidized bed

Nitrogen evolution was studied during the co-combustion of hydrothermally treated municipal solid wastes (HT MSW) and coal in a bubbling fluidized bed (BFB). HT MSW blending ratios as 10%, 20% and 30% (wt.%) were selected and tested at 700, 800, 900 °C. Emissions of NO and N₂O from blends were measured and compared with the results of mono-combustion trials. Moreover, concentrations of precursors like NH₃ and HCN were also quantified. The results are summarized as follows: NO emissions were predominant in all the cases, which rose with increasing temperature. The blending of HT MSW contributed to the NO reduction. N₂O emissions decreased with temperature rising and the blending of HT MSW also presented positive effects. At 30% HT MSW addition, both NO and N₂O emissions showed the lowest values (391.85 ppm and 55.33 ppm, respectively at 900 °C). For the precursors, more HCN was detected than NH₃ and both played important roles on the gas side nitrogen evolution.     

Full-scale blending treatment of fresh MSWI leachate with municipal wastewater in a wastewater treatment plant

Fresh leachate, generated in municipal solid waste incineration (MSWI) plants, contains various pollutants with extremely high strength organics, which usually requires expensive and complex treatment processes. This study investigated the feasibility of blending treatment of MSWI leachate with municipal wastewater. Fresh MSWI leachate was pretreated by coagulation–flocculation with FeCl₃ 2 g/L and CaO 25 g/L, plate-and-frame filter press, followed by ammonia stripping at pH above 12. After that, blending treatment was carried out in a full-scale municipal wastewater treatment plant (WWTP) for approximately 3 months. Different operational modes consisting of different pretreated leachate and methanol addition levels were tested, and their performances were evaluated. Results showed that throughout the experimental period, monitored parameters in the WWTP effluent, including COD (<60 mg/L), BOD₅ (<20 mg/L), ammonium (<8 mg/L), phosphorus (<1.5 mg/L) and heavy metals, generally complied with the Chinese sewage discharged standard. Under the experimental conditions, a certain amount of methanol was needed to fulfill TN removal. An estimation of the operation cost revealed that the expenditure of blending treatment was much lower than the total costs of respective treatment of MSWI leachate and municipal wastewater. The outcomes indicated that blending treatment could not only improve the treatability of the MSWI leachate, but also reduce the treatment cost of the two different wastewaters.     

Nitrogen fixation estimates for the Baltic Sea indicate high rates for the previously overlooked Bothnian Sea

Dense blooms of diazotrophic filamentous cyanobacteria are formed every summer in the Baltic Sea. We estimated their contribution to nitrogen fixation by combining two decades of cyanobacterial biovolume monitoring data with recently measured genera-specific nitrogen fixation rates. In the Bothnian Sea, estimated nitrogen fixation rates were 80 kt N year⁻¹, which has doubled during recent decades and now exceeds external loading from rivers and atmospheric deposition of 69 kt year⁻¹. The estimated contribution to the Baltic Proper was 399 kt N year⁻¹, which agrees well with previous estimates using other approaches and is greater than the external input of 374 kt N year⁻¹. Our approach can potentially be applied to continuously estimate nitrogen loads via nitrogen fixation. Those estimates are crucial for ecosystem adaptive management since internal nitrogen loading may counteract the positive effects of decreased external nutrient loading.     

Assessment of the maximum allowed acid deposition load at current stage in China

Soil acidification caused by acid deposition has been significant in some forests in southern China. We present an approach for assessing the current stage maximum allowed load (SML) of acid deposition for terrestrial system in the country. The main idea was that soil base cation exchange as a finite buffer to acidity was included in the soil acidity mass balance calculation at current acidification stage. We calculated the SML for five forests in southern China. The usual critical loads for the same forests were also calculated by the steady state mass balance model for comparison. The results showed that the SML is a more tolerant limit than the critical load for the forests with soils not acidified seriously at current stage. However, the SML become a more stringent limit to acid deposition when the forest soils have acidified seriously to very low base cation saturation. In this case the SML assessment is beneficial for the soils recovering from a serious acidified state. Based on a national scale database, the SML mapping for non-agricultural soil system in China was carried out.     

工业园区综合难降解废水深度处理实验研究

某工业园区综合废水处理厂设计规模5.0×104m3/d,原设计出水执行《城镇污水处理厂污染物排放标准》(GB 18918-2002)一级B标准,需将出水标准提高到一级A排放标准.分别采用混凝沉淀法和高级氧化法深度处理二级生化出水.小试试验结果表明:二级生化出水CODcr在62~75 mg/L左右,PAC、Al2(SO4)3及PFS三种絮凝沉淀药剂处理出水CODcr去除效果均不明显,不能稳定达到一级A排放标准.芬顿催化氧化的pH=5,FeSO4+H2O2投加量为(200+100)mg/L;臭氧氧化的O3投加量33 mg/L,其出水CODcr均能达到一级A排放标准.     

亚微米颗粒在Sierpinski海绵模型中热泳沉积研究

亚微米颗粒由于其特殊的粒径尺度,具有很多不同于与传统细颗粒的物理和化学性质,同时极易吸入人体,对人体造成很大危害。谢尔宾斯基海绵模型作为一种理想化的结构模型,具有内比表面积大、多通道等特点。通过建立可工程应用的谢尔宾斯基海绵模型通道,并结合热泳沉积相关数学模型开展计算,可以发现:随着谢尔宾斯基海绵阶数的上升,内部通道的增加是引起亚微米颗粒热泳沉积率上升的主要因素;在海绵通道中运动的亚微米颗粒较之其他粒径的颗粒,更容易受到热泳沉积的影响;同时温差对其热泳沉积影响较为剧烈,呈现线性变化。建立具有工程特征的谢尔宾斯基海绵模型通道,可为研究亚微米颗粒沉积及脱除开辟一条新途径。     

人造沸石负载纳米氧化镁同步脱氮除磷的研究

氮、磷是引发水体富营养化的限制性因素,控制水体中的氮、磷总量可以有效抑制水体富营养化的产生。以人造沸石为研究对象,探究不同改性方法对人造沸石同步去除水中氮、磷的影响。主要工艺为高温碱(NaOH)浸改善沸石结构,高温盐浸(MgCl)负载纳米态氧化镁。结果表明改性的最佳条件为:两阶段的烘干温度45℃;NaOH溶2+3-液浓度0.5 mol/L;MgCl溶液的浓度1 mol/L。对NH-N和PO的去除效率分别可达到83.76%和74.24%。对人造沸石2 4 4的热稳定性进行了实验,其烧失量达40.6%。最后,对吸附饱和的人造沸石进行脱附实验,脱附剂的选择为NaCl、KCl以及+3-两者的混合液。NaCl对NH4+-N和PO43-都有较为明显的脱附效果,脱附率分别可达84.54%和59.35%。     

厌氧氨氧化工艺脱氮及其污泥形态的研究

为研究厌氧氨氧化工艺对高浓度含氮废水的脱氮性能,在以聚乙烯海绵作为填料的上流式厌氧固定床反应器中利用人工配置高浓度含氮废水进行了实验研究.实验中通过添加充足无机碳源,实现了厌氧氨氧化反应器在总氮浓度900～1 210 mg/L长期稳定的运行,脱氮效率在80％以上,最高氮负荷为5.9 kg/m3·d.结果表明:充足的无机碳源在一定程度上可有效地降低高浓度亚硝氮对厌氧氨氧化菌的抑制作用.通过对污泥性状的研究,明确寻找出污泥上浮的原因所在.通过Stover-Kincannon模型确定系统动力学参数KB和Umax分别为30.2 g/L·d和2L2g/L·d,这将有助于对该厌氧氨氧化系统各控制条件的有效调节和准确设定,也为日后应用于实际工程中提供重要的理论依据.     

模拟氮沉降和CO2浓度增加对三江平原小叶章群落土壤总有机碳和氮素含量的影响

利用开顶气室(Open-Top Chamber,OTC),设置当前大气CO2浓度(370μmol.mol-1)、中等CO2浓度(550μmol.mol-1)和高CO2浓度(700μmol.mol-1)3个CO2浓度水平和不施氮(N1,0g N.m-2.a-1)、常氮(N2,5g N.m-2.a-1)、高氮(N3,10g N.m-2.a-1)3个氮素水平。研究了不同N沉降水平下,大气CO2浓度升高对以三江平原小叶章群落土壤有机碳和氮素含量的影响。结果表明:CO2浓度升高结合氮沉降连续运行两个生长季后,湿地土壤总有机碳含量没有显著变化,说明较短时间内大气CO2浓度升高和氮沉降不会使三江平原土壤有机碳含量产生变化。氮沉降引起各个土层的土壤全氮、铵态氮和硝态氮的含量增加,施氮水平越高土壤氮增加越多,但是全氮增加量不明显,铵态氮随施氮量的增加呈现极显著差异水平(P<0.01)。0～10cm,10～20cm土层土壤全氮、铵态氮的含量随着CO2浓度升高呈现出先增大后减小的趋势。土壤硝态氮含量在10～20cm土层含量变化与土壤全氮、铵态氮的变化趋势相同。说明大气CO2浓度一定程度的增加可以增加土壤的氮素含量,但是过量的大气CO2浓度反而会使得土壤氮素含量减少。     

城市排水系统沉积物特性研究

重点阐述了沉积物的来源和组成,沉积物的颗粒粒径、有机物含量(VSS/SS)、颗粒粘性和颗粒密度等物化性质,以及附着于沉积物上的金属污染物的相关特征。其粒度分布范围是D10为1.89～223.21μm,D50为12.38～437.30μm,D90为39.06～1 572.52μm;VSS/SS的范围是1%～38%;密度范围是1.80～2.47 g/cm3。金属污染物主要的附着对象是沉积物中的细小颗粒如生物膜上。以上沉积物性质对于解决排水系统的泥沙淤积问题以及水体污染的控制都具有重要意义。