反渗透海水淡化的操作压力为何必须明显超过海水渗透压，而不能恰好等于渗透压来节省能耗？
In reverse-osmosis seawater desalination, why must operating pressure sit well above the osmotic pressure of seawater instead of exactly matching it to save pumping energy?
直答：跨膜水通量取决于净驱动压力ΔP−Δπ，压力恰好等于渗透压时通量为零，一滴淡水也产不出。机理：反渗透膜表皮层选择性透水并截留溶解盐，通量近似为J=A(ΔP−Δπ);运行中回收率升高使进料持续浓缩，浓差极化又令膜面盐度高于主体水流，局部渗透压进一步抬高，加上管路与元件的沿程损失，实际操作压力必须在渗透压之上留足裕量，现代装置靠能量回收设备控制能耗。
Water flux across the membrane scales with the net driving pressure ΔP−Δπ; at a pressure merely equal to osmotic pressure the flux is zero and no permeate is produced. An RO membrane's skin layer passes water selectively and rejects dissolved salts, giving a flux close to J=A(ΔP−Δπ). As recovery rises the feed concentrates, concentration polarization lifts the surface salinity above the bulk flow, local osmotic pressure climbs further, and friction losses add on top, so plants operate with ample margin above osmotic pressure while energy-recovery devices keep power demand acceptable.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
S. Sourirajan《Reverse Osmosis》，Academic Press，1970年（基于Loeb-Sourirajan非对称醋酸纤维素膜研究）
S. Sourirajan, Reverse Osmosis, Academic Press, 1970, building on the Loeb-Sourirajan asymmetric cellulose acetate membrane
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780236308385 (1970)
#反渗透 #渗透压 #海水淡化
城市给排水工程包含什么？
What does urban water supply and drainage include?
它涵盖取水、净水、输配水管网（给水）以及污水收集、处理与排放或回用（排水），保障饮水安全与水环境健康。
It covers intake, treatment and distribution (supply) plus sewage collection, treatment and reuse (drainage), safeguarding drinking water and the environment.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
AWWA 给水工程手册；Metcalf & Eddy《废水工程》
AWWA Water Treatment/Distribution manuals; Metcalf & Eddy, Wastewater Engineering
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL3866635W：Wastewater engineering（
#土木 #给排水
混凝剂投加中同时存在'欠量无效'与'过量再稳'两个失效区,其胶体化学机理分别是什么?运行上如何避开这两个区间?
Coagulant dosing has two failure zones — underdosing that accomplishes nothing and overdosing that restabilizes the suspension. What colloid-chemical mechanism drives each, and how do operators steer clear of both?
投加不足时,铝盐/铁盐水解产物的正电荷不足以中和颗粒表面负电荷,Zeta 电位仍远离等电点,静电排斥维持胶体稳定,矾花难以形成;投加过量时颗粒表面吸附多余正电荷发生电荷反转,Zeta 电位由负转正、斥力重新占优,即再稳现象。中等剂量下则进入卷扫絮凝区,大量氢氧化物沉淀网捕细颗粒形成粗大絮体。因此最佳投药量应以 Zeta 电位滴定配合烧杯搅拌试验确定,并根据原水浊度和碱度动态调整。
When dosing is too low, the positive hydrolysis products of aluminum or iron salts fail to neutralize negative particle surfaces, the zeta potential stays far from the isoelectric point, electrostatic repulsion persists, and no floc forms. When dosing is excessive, particles adsorb surplus positive charge until the potential reverses sign, repulsion dominates again, and the suspension is restabilized. Intermediate doses enter the sweep-flocculation regime, where bulky hydroxide precipitates enmesh fine particles into large flocs, so the optimum dose must be set from zeta-potential titration backed by jar tests and adjusted for raw-water turbidity and alkalinity.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Duan J, Gregory J. Coagulation by hydrolysing metal salts[J]. Advances in Colloid and Interface Science, 2003, 100-102: 475-502.
J. Duan and J. Gregory, 'Coagulation by hydrolysing metal salts', Advances in Colloid and Interface Science, vols. 100-102, pp. 475-502, 2003.
独立核验依据 · Independent verification: 核验依据 1 DOI 10.1016/s0001-8686(02)00067-2
#混凝 #Zeta电位
二沉池污泥沉降性能恶化时,为什么要结合 SVI 与镜检来判断丝状菌膨胀的诱因,而不能只看 MLSS 浓度?
When sludge settleability in the secondary clarifier deteriorates, why must filamentous bulking be diagnosed with SVI together with microscopic examination rather than by MLSS concentration alone?
SVI 只定量反映沉降性能恶化的程度,MLSS 更只是常规运行参数,二者都无法指明膨胀机理。镜检能识别丝状菌类型:低溶解氧常滋生球衣菌,低负荷利于微丝菌生长,高硫酸盐浓度则诱发发硫菌过度繁殖,不同类型对应的调控方向完全不同。只有确认诱因后,才能针对性地提高曝气量、调整泥龄或补充营养盐,避免盲目排泥拖长恢复周期。
SVI only quantifies how far settleability has degraded, and MLSS is just a routine operating parameter; neither reveals the mechanism behind the bulking. Microscopy identifies the filament type: low dissolved oxygen favors Sphaerotilus natans, low food-to-microorganism ratio promotes Microthrix parvicella, and elevated sulfate levels trigger Thiothrix overgrowth — each demanding different corrective actions. Only once the cause is identified can operators raise aeration, adjust sludge age or dose nutrients, instead of wasting sludge blindly and prolonging recovery.
难度 进阶 · 适合 大众
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录仅给书名，无版次与年份；同一书名常对应多个版次，不臆测具体版本。
Metcalf & Eddy《废水工程:处理与回用》第4版 活性污泥法运行问题章节
Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery, activated-sludge bulking chapter
#活性污泥法 #污泥膨胀诊断
自来水厂往原水里投加硫酸铝后，为什么原本久悬不沉的细小胶体颗粒会迅速聚集长大成可沉淀的絮体？
After a water plant doses raw water with aluminum sulfate, why do tiny colloidal particles that had stayed suspended indefinitely rapidly clump into large settleable flocs?
直答：铝盐的水解产物中和了胶体表面的负电荷并提供吸附架桥，脱稳后的颗粒一经碰撞便互相黏结长大。机理：天然水体胶体因双电层静电排斥而长期稳定;硫酸铝数秒内水解生成带正电的多核羟合铝配合物，压缩双电层、吸附电中和使ζ电位趋零，投量较高时新生氢氧化铝还能网捕卷扫颗粒。缓慢搅拌提供有效碰撞机会，絮体长大后经沉淀或气浮分离。
Alum hydrolysis products neutralize the negative colloid surface charge and bridge between particles, so once destabilized the particles stick together on every effective contact. Natural colloids persist because electric double-layer repulsion keeps them apart; dosed alum hydrolyzes within seconds into positively charged polynuclear hydroxo-aluminum species that compress the double layer and neutralize charge, driving the zeta potential toward zero, while at higher doses freshly formed aluminum hydroxide sweeps particles down en masse. Gentle flocculation mixing supplies the collisions until flocs grow large enough to settle or float out.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-04
来源 · Source
W. Stumm, C. R. O'Melia,《Stoichiometry of Coagulation》,Journal AWWA,1968 (DOI: 10.1002/j.1551-8833.1968.tb03579.x)
W. Stumm and C. R. O'Melia, 'Stoichiometry of Coagulation', Journal AWWA, 1968, DOI: 10.1002/j.1551-8833.1968.tb03579.x
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1002/j.1551-8833.1968.tb03579.x
#混凝 #胶体脱稳 #双电层