Utafiti huu unatengeneza mfumo wa maabara unaotegemea humidification–dehumidification, yaani HDH, kwa ajili ya kurejesha maji kutoka oily wastewater ambayo huwa ngumu kutenganishwa kwa methods za kawaida kutokana na oil droplets na surfactants. Katika system, heated oily water inasprayiwa downward juu ya porous packing material huku air ikisogea upward katika opposite direction. Water vapor inaingia kwenye air, nonvolatile oil components zinabaki kwenye liquid phase, na humid air inapozwa katika section tofauti na kubadilishwa kuwa product water. Model wastewater yenye %1 oil ilipoprocessiwa katika 80 °C, system ilitoa 12 L·hour⁻¹ product water na 50 L·m⁻³·hour⁻¹ volumetric productivity; COD ya product water ilikuwa 15 mg·L⁻¹, na reported COD retention rate ilikuwa %99,8.

Feed temperature ilipoongezeka kutoka 60 °C hadi 85 °C, volumetric water productivity kwa %1 oily water iliongezeka kutoka 25,4 hadi 53,8 L·m⁻³·hour⁻¹, ongezeko la takriban %112. Kinyume chake, katika 80 °C kuongeza oil concentration kutoka %0 hadi %10 kulipunguza productivity kutoka takriban 51,3 hadi 33,3 L·m⁻³·hour⁻¹, kupunguza gain output ratio kwa %41 na kuongeza reported specific thermal energy consumption kwa %72 hadi 2309 kWh·m⁻³. Kuongeza Tween 80 kulifanya emulsion iwe stable zaidi na kupunguza water production kwa takriban %2,5 ikilinganishwa na %1 oily water.

Results za study zinaonyesha HDH system inaweza kuhifadhi nonvolatile oil components kwa kiasi kikubwa katika concentrated liquid phase. Hata hivyo, experiments zilitumia model mixtures zilizoandaliwa kwa food-grade soybean oil na Tween 80 badala ya real refinery au oil-field wastewater. Kila experiment ilihusu one-hour steady operating period pekee; long-term fouling, foaming, corrosion, oil accumulation, surfactant transport na equipment durability hazikuchunguzwa. Energy calculation pia haijumuishi kikamilifu pump, fan, cooling water na heat losses katika full-system level.

Kwa mtazamo wa Uturuki: Approach ina research value kwa refinery na petrochemical facilities, metalworking na machining, vegetable-oil production, food industry, ports, shipyards, maritime transport na facilities zinazozalisha oily process water nchini Uturuki. Kabla ya application, mineral oil, emulsifier, detergent, salt, suspended solids, heavy metals na volatile organic compounds katika local wastewaters zinapaswa kucharacterizeiwa separately. Integration with waste heat, solar heat au cogeneration heat; mist eliminators za kupunguza droplet carryover; management ya concentrated oily residue na advanced treatment ya product water zinapaswa kutathminiwa pamoja. Kutokana na study hii haiwezi kuhitimishwa kwamba system itafikia same %99,6–99,8 COD retention rate kwa oily wastewaters zote nchini Uturuki, itazalisha direct-discharge au reuse water, au itakuwa economically superior kuliko existing methods.

Kwa nini oily wastewater ni ngumu kutenganisha?

Katika industrial oily waters, oil haipo kila mara kama free layer rahisi kukusanywa kwenye surface. Mechanical mixing, pumps, detergents na surfactants zinaweza kuvunja oil kuwa micro- au nano-scale droplets. Droplets hizi zinaweza kubaki suspended in water kwa muda mrefu na kutengeneza stable emulsions.

Density-difference-based settling na centrifugation zinaweza kuwa effective kwa large free-oil droplets, lakini zikawa insufficient kwa small stable droplets. Membranes zinaweza kutoa high separation precision; hata hivyo adsorption ya oil kwenye membrane surface, pore blocking na hard-to-recover flux losses zinaweza kuongeza operating cost. Chemical coagulation na emulsion-breaking methods zinaweza kusababisha chemical consumption na secondary sludge.

Watafiti walichunguza thermal-separation approach inayohamisha water selectively kwenda vapor phase badala ya kujaribu kupitisha oil kwenye filter. Basic assumption ni kwamba katika experimental temperatures, vapor pressure ya water huongezeka strongly huku tendency ya soybean-oil components kuingia vapor phase ikibaki very low.

Humidification–dehumidification inafanyaje kazi?

HDH ni imitation ya natural water cycle ndani ya closed device. Process ina two main sections:

1. Humidification: Heated liquid inasprayiwa juu ya porous packing material. Liquid inapotengeneza thin film na small droplets, counterflowing air inachukua water vapor.
2. Dehumidification: Hot humid air inatumwa kwenye condenser. Cooled water vapor inakuwa liquid na kukusanywa kwenye product-water tank.

Nonvolatile components kama oil na surfactant zinabaki kwa kiasi kikubwa katika liquid inayorudi kwenye feed tank. Hivyo system haizalishi water pekee, bali pia inapunguza volume ya remaining stream na kuconcentrate oil components.

System iliendeshwa katika atmospheric pressure na feed temperatures 60–85 °C. Temperature range hii inaweza kuruhusu matumizi ya lower-temperature waste heat ikilinganishwa na high-pressure evaporation systems. Hata hivyo, katika experimental setup iliyochunguzwa, heat ilitolewa na electric heater; real waste-heat au solar-heat source haikutumika.

Oil layer inazuia evaporation vipi?

Continuous oil film inapoundwa juu ya water, film hii inatengeneza physical barrier kati ya water molecules na carrier air. Water molecules lazima kwanza zipite kwenye oil layer au zifikie gas phase kupitia regions zilizoachwa open na film. Oil fraction inapoongezeka, viscosity ya liquid na mass-transfer resistance katika gas–liquid interface huongezeka.

Kulingana na mechanism iliyopendekezwa katika Figure 4, oil film si completely stationary. Shear force ya upward-moving air, movement ya liquid juu ya packing na surface tension zinastretch, deform na wakati mwingine kuvunja oil film. Water vapor inaweza kupita kwenye gas phase kupitia temporary openings hizi.

Kwa hiyo system haisimami kabisa katika presence of oil, lakini inaonyesha lower productivity kuliko pure water at same temperature. Katika system yenye %1 oil, productivity katika 80 °C ilikuwa takriban %2,5 lower than pure water, na hii ilihusishwa na interfacial resistance hiyo.

Model oily waters ziliandaliwaje?

Research ilitumia deionized water, food-grade soybean oil na analytical-grade Tween 80 badala ya real industrial wastewater. Two feed systems ziliandaliwa:

Katika samples zenye surfactant, %0,5 Tween 80 ilitumika kwa %1 oil; %1,5 kwa %3 oil; %2,5 kwa %5 oil; %3,5 kwa %7 oil na %5 kwa %10 oil. Kila feed group iliandaliwa kwa volume 200 liters ili kusaidia continuous operation ya recirculating system.

Text inaita water “dispersed phase” katika systems zote mbili. Hata hivyo, mixtures zina water kwa majority kubwa, Figure 1(c) inaonyesha oil droplets zikiwa dispersed ndani ya continuous liquid, na discussion yote inatumia mechanism ya “oil droplets in water”. Kwa hiyo phase definition si terminologically consistent ndani ya text.

Main components za experimental setup

Laboratory system ina feed tank, electric heater, circulation pump, humidification tower, dehumidification tower, cooling-water tank, condenser, product-water tank na variable-speed fan. Humidification na dehumidification chambers zilitengenezwa kwa polypropylene na outer surfaces zikafunikwa kwa thermal insulation.

Katika towers, porous polypropylene spheres zenye diameter 3,8 cm zilitumika kama packing material. Heated liquid ilisprayiwa kutoka juu na ikaflow downward over packing huku air ikisogea upward kutoka chini. Countercurrent arrangement hii ililenga kuongeza contact area na contact time kati ya air na liquid.

Feed ilicirculateiwa kwa GP-125 pump yenye nominal capacity 2100 L·hour⁻¹; katika experiments flow rate iliwekwa 1000 L·hour⁻¹. Nominal air flow ya FD-250 fan ni 2100 m³·hour⁻¹. Katika result experiments, feed-to-air mass-flow ratio, yaani MFR, iliwekwa 4,8.

Cooling-water flow katika dehumidification section iliwekwa constant 1000 L·hour⁻¹. Humid air ilipo-contact condenser tubes ilipozwa na condensed water ikakusanywa katika separate tank.

Experiments zilidumu kwa muda gani?

Kila experiment iliendelea baada ya system kufikia steady state hadi one-hour operating period ikamilike. Kila condition ilirudiwa at least three times. Product-water mass ilipimwa kwa electronic balance yenye precision ±0,1 g; chemical oxygen demand ya feed na product water ilibainishwa kwa full-spectrum rapid water analyzer.

Ingawa at least three repeats zilifanywa, result graphs hazina error bars, na standard deviation au confidence interval hazikutolewa pamoja na mean values. Statistical-significance test kwa differences between groups pia haikufanywa. Kwa hiyo magnitude ya small differences, hasa approximately %2,5 productivity change iliyosababishwa na surfactant, relative to experimental scatter haiwezi kutathminiwa.

Mass na energy balance

Simplified mass balance iliyotumika kwa system ni:

\[ \dot{m}_{\mathrm{in}}-\dot{m}_{\mathrm{out}} = \dot{m}_{\mathrm{pw}} \]

Hapa \(\dot{m}_{\mathrm{in}}\) ni mass flow ya feed entering system, \(\dot{m}_{\mathrm{out}}\) concentrated outlet, na \(\dot{m}_{\mathrm{pw}}\) product water.

Heat input katika study ilihesabiwa kwa equation hii:

\[ Q_{\mathrm{in}} = \dot{m}_{\mathrm{in}} \left( c_{p,1}T_{\mathrm{feed},1} - c_{p,2}T_{\mathrm{feed},2} \right) \]

Equation hii inategemea difference kati ya inlet na outlet enthalpies za feed stream. Analysis inachukulia system ni sealed, steady state na atmospheric pressure; heat losses, secondary heat transfer katika packing na device body, pamoja na density effects zinaweza kupuuzwa.

Katika real industrial system, heat losses, electricity ya pump na fan, cooling-water production, motor efficiencies na auxiliary equipment zinaathiri total energy consumption. Kwa hiyo energy values katika study zinapaswa kusomwa kama idealized thermal-performance indicators, si full-plant electricity na fuel consumption.

Volumetric separated-water productivity

Volumetric separated-water productivity inaonyesha product-water flow per effective volume ya dehumidification section:

\[ \mathrm{VSWP} = \frac{V_{\mathrm{pw}}}{V_{\mathrm{dc}}} \]

Hapa \(V_{\mathrm{pw}}\) ni product water inayopatikana per unit time, na \(V_{\mathrm{dc}}\) ni effective dehumidification volume ya takriban 0,24 m³. Kwa mfano 12 L·hour⁻¹ product water inatoa:

\[ \frac{12\ \mathrm{L\,h^{-1}}} {0{,}24\ \mathrm{m^3}} = 50\ \mathrm{L\,m^{-3}\,h^{-1}} \]

.

COD retention rate

Transfer ya organic pollutants kwenda product water ilitathminiwa kupitia chemical oxygen demand:

\[ R_c = \left( 1-\frac{f_{\mathrm{COD}}}{w_{\mathrm{COD}}} \right)\times100\% \]

\(f_{\mathrm{COD}}\) ni COD ya product water, na \(w_{\mathrm{COD}}\) ni COD ya feed. Ratio hii inaonyesha retention ya organic matter upande wa feed; si directly oil-mass separation percentage. Dissolved organic components kama Tween 80 pia zinachangia COD measurement.

Gain output ratio

Gain output ratio ni ratio ya latent heat inayorecoveriwa kwa condensation ya product water kwa heat supplied to system:

\[ \mathrm{GOR} = \frac{ \rho_{\mathrm{pw}} V_{\mathrm{pw}} h_{\mathrm{pw}} }{ Q_{\mathrm{in}} } \]

GOR inapoongezeka, supplied heat inachukuliwa kutumika more effectively katika product-water production. Study inatoa GOR 0,50 kwa pure water na 0,47 kwa %1 oily water katika 80 °C. Values zote mbili ni below one; system inafanya kazi bila multi-stage heat recovery.

Specific thermal energy consumption

STEC equation katika study ni:

\[ \mathrm{STEC} = \frac{ Q_{\mathrm{in}} }{ 3600V_{\mathrm{pw}} } \]

STEC inalenga kuonyesha thermal-energy consumption per cubic meter of product water katika kWh·m⁻³. Hata hivyo, katika nomenclature section \(V_{\mathrm{pw}}\) imefafanuliwa katika L·hour⁻¹. Kwa kuwa factor 1000 ya kuconvert liters kwenda cubic meters haijaonyeshwa explicitly katika equation, kuna unexplained unit conversion kati ya formula na reported unit.

Reported values katika 80 °C ni 1345 kwa pure water na 1410 kWh·m⁻³ kwa %1 oily water. Katika %10 oil value ni 2309 kWh·m⁻³. Values hizi kubwa zinaonyesha matumizi ya low-cost au waste heat yatakuwa critical kwa economic feasibility.

Nini kilitokea oil concentration ilipoongezeka?

Feed temperature ikiwa 80 °C, liquid flow 1 m³·hour⁻¹ na MFR 4,8, kuongeza oil concentration kuliathiri vibaya main performance indicators zote.

Oil fraction ilipoongezeka, viscosity ya liquid film iliyoundwa juu ya packing iliongezeka, spreading ya liquid na effective contact area with air zikapungua. Wakati huo huo accumulation ya oil katika gas–liquid interface iliunda additional resistance dhidi ya transfer ya water molecules kwenda vapor phase.

Evaporation ya oil components wenyewe kwenda product ilichukuliwa kuwa low. Increase ya COD katika product water ilihusishwa na small liquid droplets zilizobebwa na humid air. Interpretation hii inaonyesha kuongeza suitable demister au mist eliminator kwenye humidifier outlet kunaweza kuboresha product-water quality; lakini study haikufanya equipment comparison ya aina hiyo.

Nini kilitokea feed temperature ilipoongezeka?

Kwa %1 oily feed, kuongeza temperature kutoka 60 °C hadi 85 °C kuliongeza vapor pressure ya water na amount of moisture ambayo air inaweza kubeba. Results ni:

Ingawa more heat iliingizwa kwenye system katika higher temperature, reported thermal-energy consumption per unit product ilipungua kwa sababu product-water quantity iliongezeka faster. Hata hivyo, temperatures above 85 °C hazikuchunguzwa na limits kama material durability na foaming hazikusomwa.

Kwa nini surfactant ilipunguza performance?

Tween 80 ilipunguza oil–water interfacial tension na kutengeneza smaller na more stable oil droplets. Surfactant layer inayozunguka droplet iliunda steric barrier, ikifanya coalescence ya droplets na separation into larger phases kuwa ngumu zaidi.

Katika 80 °C, water production kwa feed yenye %1 oil na %0,5 Tween 80 ilikuwa takriban %2,5 lower than surfactant-free %1 oily feed. Product-water COD iliongezeka kutoka 15 hadi 28 mg·L⁻¹, na retention rate ikapungua kutoka takriban %99,8 hadi %99,7.

Watafiti wanapendekeza smaller droplets zina stronger Brownian motion na zinaweza kuwa more susceptible to entrainment na upward vapor–air flow. Pia free Tween 80 iliyodissolveiwa kwenye water inaweza kuchangia COD measurement katika product water.

Figure 7 inalinganisha only VSWP na COD retention kati ya systems zenye na zisizo na surfactant. Ingawa conclusion section inasema surfactant pia iliharibu energy-use efficiency, separate GOR au STEC numbers hazikuwasilishwa katika main text.

Product-water quality inapaswa kutathminiwaje?

COD ya 15 mg·L⁻¹ ilipimwa katika product water kutoka %1 oily feed na 110 mg·L⁻¹ kutoka %10 oily feed. Kwa sababu feed concentration ni high, fractional retention inaweza kubaki above %99,8; lakini absolute COD ya product water huongezeka.

High removal percentage haimaanishi product water automatically inafaa kwa drinking, process reuse au direct environmental discharge. Study haikupima:

• Oil na grease concentration,
• Total organic carbon,
• Turbidity na suspended solids,
• Tween 80 au other surfactants,
• Volatile organic compounds,
• pH, conductivity na salinity,
• Heavy metals,
• Toxicity na biodegradability.

Kwa hiyo expression “deep treatment” inapaswa kutathminiwa only within COD-retention performance iliyopimwa katika study.

Main conclusions zinazoungwa mkono na study

• Laboratory-scale HDH system iliweza kupata condensed product water kutoka model oily waters zilizoandaliwa kwa soybean oil.
• Katika %1 oil na 80 °C, product-water flow ilikuwa 12 L·hour⁻¹ na VSWP 50 L·m⁻³·hour⁻¹.
• Katika same condition product-water COD ilikuwa 15 mg·L⁻¹ na calculated COD retention rate %99,8.
• Kuongeza feed temperature kuliongeza water productivity na GOR huku kupunguza reported STEC.
• Kuongeza oil concentration kuliongeza interfacial mass-transfer resistance na kupunguza water production.
• Surfactant ilistabilize emulsion, ikapunguza water production kwa kiasi kidogo na kuongeza product-water COD.
• Hata katika feed yenye %10 oil, calculated COD retention ilibaki above %99,8.

Study haionyeshi nini?

• Real refinery, oil-field, metalworking au maritime wastewater haikujaribiwa.
• Soybean oil ilitumika badala ya petroleum hydrocarbons; transfer ya volatile na semivolatile petroleum components kwenda product haikutathminiwa.
• Continuous operation longer than one hour, weekly au monthly stability haikuchunguzwa.
• Oil accumulation kwenye packing, biofouling, foaming na cleaning requirement hazikupimwa.
• Actual total energy consumption ya pumps, fan, cooling circuit na electric heater haikutolewa.
• No experimental integration with waste heat au solar energy ilifanywa.
• Disposal au recovery method ya concentrated oily liquid haikutathminiwa.
• Comprehensive analyses hazikuonyesha product water inakidhi official discharge au reuse standard yoyote.
• System haikulinganishwa kwa same feed na membrane, centrifuge, dissolved-air flotation au chemical emulsion breaking.
• No capital cost, operating cost, cost per water na life-cycle analysis zilifanywa.

Important ambiguities na inconsistencies katika text

Mbinu na Matokeo ya Utafiti

Source chemicals na feed composition

HDH setup

Measurement instruments

Basic experimental conditions

Main performance indicators

Results under reference condition

Effect ya oil concentration

Effect ya temperature

Effect ya surfactant

Reproducibility na scale-up requirements

Kuludia experiments at least three times ni positive methodological feature. Hata hivyo, kwa sababu standard deviations hazikutolewa pamoja na mean results, scatter ya productivity, COD, GOR na STEC measurements haijulikani. Pia haikuonyeshwa kwa separate analysis kama device inatoa same result kwa different days au separately prepared emulsion batches.

Kwa industrial scale-up, studies hizi zinahitajika:

• Long-term continuous experiments na real oily wastewaters,
• Packing fouling na cleaning procedures,
• Mist eliminator na droplet separator design,
• Heat-exchanger na heat-recovery optimization,
• Integration na waste heat na solar thermal system,
• Transfer ya volatile organic substances kwenda product water,
• Recovery au disposal ya concentrated oily residue,
• Total electricity na fuel consumption,
• Technoeconomic na life-cycle assessment.

Dokezo la Chanzo na Mbinu

Full original title ya study: Experimental Investigation of Reduction and Separation Treatment of Oily Wastewater via Humidification-Dehumidification System

Authors na order: Huiwen Chen, Jingcheng Cai, Fei Guo.

Equal contribution au co-first authorship: Hakuna equal-contribution au co-first-authorship statement katika study.

Corresponding author: Fei Guo. Ameonyeshwa kwa star kama corresponding author; email address haipo katika text.

Institution: School of Energy and Power Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China.

DOI: 10.2139/ssrn.7197880. DOI hii ni ya SSRN preprint record na si DOI ya peer-reviewed journal article.

Journal au conference: Hakuna verified peer-reviewed journal au conference publication kwa reviewed version.

Publication platform: SSRN.

Original publisher: Hakuna verified final journal publisher kwa study. SSRN ndiyo platform ambapo preprint imesambazwa.

Publication year: 2026.

Source type: Research preprint katika experimental environmental na energy engineering, thermal separation, mass transfer na oily-wastewater treatment.

Peer-review status: Study haijapitia peer review. Kila page ina warning “This preprint research paper has not been peer reviewed”.

Official links:Official SSRN record page na SSRN DOI link.

Funding: Hakuna funding information katika reviewed text.

Conflict of interest: Hakuna separate conflict-of-interest statement katika reviewed text.

Author contributions: Hakuna CRediT au detailed author-contribution statement katika reviewed text.

Data access: Hakuna open-data repository au access link kwa raw experimental data, repeat measurements, error calculations au device records.

Makala hii ya Kiswahili imeandaliwa kwa kutegemea oily-water preparation protocol, laboratory device, system photographs, emulsion micrograph, mass na energy balances, performance formulas, oil-concentration, temperature na surfactant experiments pamoja na numerical results katika Figures 1–7 za uploaded 17-page study. Hakuna new experimental result isiyokuwepo katika study au scientific-performance finding kutoka external source iliyoongezwa. External verification imewekewa kikomo na bibliographic identity ya authors, DOI, publication platform na publication status.

Main limitations za study ni lack of peer review, matumizi ya soybean oil na Tween 80 badala ya real industrial wastewater, experiments kuwa limited to one-hour steady period, absence ya error bars na statistical analyses, assessment ya product-water quality kwa COD pekee, kutokuhesabu total system energy consumption, unclear unit conversion katika STEC formula, na absence ya long-term fouling na scale-up experiments.

Results zinaonyesha kwamba chini ya laboratory conditions, HDH process inaweza kutenganisha water vapor selectively kutoka model oily water na kuhifadhi sehemu kubwa ya organic content upande wa feed. Findings si evidence ya validated energy efficiency katika real industrial plants, direct-discharge-quality water, commercial economic superiority au performance inayoweza kugeneralizeiwa kwa oily-wastewater types zote.