Iron-manganese modified recycled aggregate wetland filler and triclosan removal method

Abstract

The present application relates to the technical fields of environmental water treatment, artificial wetland filler preparation and building solid waste resource utilization, and discloses an iron-manganese modified recycled aggregate wetland filler and a triclosan removal method. The filler takes waste concrete recycled aggregate as a base body, is subjected to crushing, screening, washing and drying, and then is subjected to hydrochloric acid washing activation, sodium hydroxide alkali washing pore expansion and in-situ iron-manganese component deposition and loading in sequence, and then is dried and calcined, so that iron-manganese composite oxides are fixed on the outer surface of the aggregate and in the surface layer connected pores, and an iron-manganese active interface is formed. When water containing triclosan flows through the modified filler layer, triclosan enters the surface layer pores of the filler, and is enriched and fixed on the rough pore wall and the surface of the iron-manganese composite oxides, so as to reduce the triclosan concentration of the effluent. In the operation process of the method, no powder adsorbent or oxidant needs to be continuously added, the filler particle morphology is stable, and the method can be used for purification treatment of urban tail water, landscape water supplement and surface runoff affected by domestic source pollution.

Description

Technical Field

[0001] This invention relates to the fields of environmental water treatment, preparation of artificial wetland fillers, treatment of new pollutants, and resource utilization of construction solid waste, specifically to an iron-manganese modified recycled aggregate wetland filler and a method for removing triclosan. Background Technology

[0002] Triclosan is a common broad-spectrum antibacterial organic pollutant, mainly originating from personal care products, detergents, medical cleaning products, and domestic sewage discharge. It easily enters urban tailwater, surface runoff, river water bodies, and landscape water replenishment systems. Once in water bodies, triclosan is difficult to completely eliminate in a short period of time, and even trace levels can pose long-term risks to aquatic ecosystems. Existing wastewater treatment processes for triclosan removal are significantly affected by influent concentration, sludge adsorption state, and operating conditions, and residues may still remain in the effluent. Constructed wetlands are characterized by low construction costs, simple operation and management, and good ecological adaptability; however, commonly used wetland fillers are mainly designed for the removal of suspended solids, nitrogen and phosphorus, and conventional organic matter, lacking specific enrichment and fixation effects for trace organic pollutants like triclosan, and their removal efficiency tends to decline after long-term operation.

[0003] Recycled aggregates from construction waste are widely available and low in cost, possessing a certain degree of porosity and mechanical stability. Using them as fillers in constructed wetlands can reduce the consumption of natural sand, gravel, and ceramsite, aligning with the trend of resource utilization of construction solid waste. However, recycled aggregates from waste concrete often retain cement paste on their surface, and some pores are blocked by carbonate deposits or fine powder. Direct use results in limited effective contact area and active sites, leading to a weak affinity for triclosan. Existing modifications of construction waste aggregates primarily target phosphorus adsorption, ammonia nitrogen removal, or general organic matter reduction. Iron oxide and manganese oxide modifiers often use ceramsite, zeolite, or activated carbon as carriers, making it difficult to simultaneously address the needs of construction solid waste utilization, wetland bed stability, and continuous triclosan purification. Summary of the Invention

[0004] To address the problems of excessive surface slurry residue, insufficient pore connectivity, and weak affinity for trace organic pollutants such as triclosan when waste concrete recycled aggregate is directly used as constructed wetland filler, this invention provides an iron-manganese modified recycled aggregate wetland filler and a method for triclosan removal. This method first removes weakly bound cement slurry and carbonate blockages from the aggregate surface through acid washing, then opens some surface pores through alkaline washing, allowing an iron-manganese mixed salt solution to enter the outer surface and shallow pores of the aggregate. Subsequently, through in-situ precipitation, aging, drying, and calcination, the iron-manganese composite oxide is fixed at the rough pore walls of the aggregate, forming an active iron-manganese interface for triclosan enrichment and fixation.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a wetland filler made of iron-manganese active interface modified construction waste recycled aggregate, wherein the filler comprises construction waste recycled aggregate that has undergone acid-base coupling activation treatment and is loaded with iron-manganese composite oxides; the construction waste recycled aggregate is aggregate particles obtained by crushing, screening and washing waste concrete, with a particle size of 2-8 mm; the acid-base coupling activation treatment includes acid washing activation treatment and alkali washing pore-expanding treatment, and the iron-manganese composite oxide is formed by in-situ precipitation of iron salts and manganese salts on the outer surface and surface interconnected pores of the construction waste recycled aggregate after acid-base coupling activation.

[0006] The preparation method of the iron-manganese active interface modified construction waste recycled aggregate wetland filler includes the following steps: crushing, screening, washing and drying waste concrete construction waste to obtain pretreated construction waste recycled aggregate; placing the pretreated construction waste recycled aggregate in hydrochloric acid solution for acid washing and activation, rinsing to near neutral and drying after acid washing; placing the acid-activated construction waste recycled aggregate in sodium hydroxide solution for alkaline washing and pore expansion, rinsing and drying to obtain acid-base coupled activated construction waste recycled aggregate; then placing the acid-base coupled activated construction waste recycled aggregate in iron-manganese mixed salt solution for immersion, adjusting the solution pH to allow iron-manganese components to precipitate in situ on the outer surface of the aggregate and in the surface interconnected pores; finally, after solid-liquid separation, drying and calcination, the iron-manganese active interface modified construction waste recycled aggregate wetland filler is obtained.

[0007] Further, the concentration of the hydrochloric acid solution is 0.5–1.5 mol / L, and the acid washing time is 2–4 h; the concentration of the sodium hydroxide solution is 1.0–2.0 mol / L, the alkaline washing temperature is 60–80 °C, and the alkaline washing time is 3–5 h; the molar ratio of iron to manganese in the iron salt and manganese salt is 2:1–4:1, and the total concentration of metal ions in the mixed salt solution formed by the iron salt and manganese salt is 0.05–0.30 mol / L; the BET specific surface area of ​​the iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler is 8.0–11.5 m² / g, the pore volume is 0.035–0.055 cm³ / g, the Fe content in the filler is 15–22 mg / g, and the Mn content is 4.5–8.0 mg / g; the aggregate after iron-manganese loading is calcined at 300–400 °C for 2–3 h to transform the iron-manganese hydroxide precursor layer into an iron-manganese composite oxide active layer.

[0008] This invention also provides a method for removing triclosan from water using the above-mentioned iron-manganese active interface modified construction waste recycled aggregate wetland filler. The filler is filled into the reaction zone of a vertical flow, horizontal subsurface flow, or combined flow constructed wetland to form a modified filler layer. Before use, the modified filler layer is pre-washed with clean water to remove fine particles, residual salts, and a small amount of unstable iron-manganese components. Then, the triclosan-containing water to be treated is introduced into the constructed wetland reaction zone, allowing the water to flow through the modified filler layer for a set hydraulic retention time. After entering the interconnected pores of the filler surface with the water flow, triclosan is enriched and fixed on the rough pore walls and the surface of the iron-manganese composite oxide, thereby reducing the triclosan concentration in the effluent. The filling thickness of the modified filler layer can be 40–80 cm, the hydraulic retention time can be 6–12 h, and the influent triclosan concentration in the water to be treated can be 0.1–50 μg / L.

[0009] The beneficial effects of this invention are as follows:

[0010] 1. This invention uses recycled aggregate from waste concrete as the wetland filler matrix. Through acid-base coupling activation and iron-manganese composite oxide loading treatment, an iron-manganese active interface is formed on the outer surface of the aggregate and in the surface interconnected pores. This allows the recycled aggregate to not only serve as a supporting filler but also to enrich and fix triclosan, and can reduce the amount of natural sand, gravel, ceramsite, and other fillers used.

[0011] 2. In this invention, acid washing and alkali washing are performed sequentially. Acid washing first removes loose slurry and carbonate blockages from the aggregate surface, exposing the covered pores. Alkali washing then enters the exposed surface pores to further roughen the pore walls. This treatment method is suitable for the characteristics of waste concrete recycled aggregate, which has a lot of residual slurry on the surface and is prone to pore blockage, and is conducive to the subsequent entry of iron and manganese components into the shallow pores of the aggregate.

[0012] 3. In this invention, the iron and manganese components precipitate in situ on the outer surface of the aggregate and within the interconnected pores of the surface layer after acid-base coupling activation, and then form an active layer of iron and manganese composite oxides through aging and low-temperature calcination. When water flows through the packing layer, triclosan can enter the surface pores and be enriched and fixed on the rough pore walls and the surface of the iron and manganese composite oxides, so that the packing can maintain a relatively stable treatment effect even under low-concentration triclosan influent conditions.

[0013] 4. The preparation process of this filler mainly includes soaking, rinsing, impregnation, pH adjustment, aging, drying, and low-temperature calcination. It does not require re-granulation of construction waste aggregate, nor does it require continuous addition of powdered adsorbents or oxidants during wetland operation. The resulting filler retains the granular shape of recycled aggregate, making it convenient to lay as the main filler in vertical flow, horizontal subsurface flow, or combined flow constructed wetlands.

[0014] 5. This filler can be used for the treatment of effluent from urban sewage treatment plants, landscape water bodies in schools and residential areas, river replenishment, and surface runoff affected by domestic pollution. While controlling triclosan pollution, it provides a wetland filler application method for the resource utilization of waste concrete aggregate. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the preparation process of the iron-manganese modified recycled aggregate wetland filler of the present invention.

[0016] Figure 2 This is a schematic diagram comparing the surface structure of the recycled aggregate before and after modification according to the present invention.

[0017] Figure 3 This is a schematic diagram of the iron and manganese composition distribution on the surface of the modified filler of the present invention;

[0018] Figure 4 This is a diagram showing the triclosan removal effect during continuous operation of the modified packing material of this invention. Detailed Implementation

[0019] The following describes the implementation process of the present invention with reference to specific embodiments. The source of raw materials, processing time, and wetland operating conditions in the embodiments can be appropriately adjusted according to the water quality and the scale of the filler material. Unless otherwise specified, they should not be construed as limiting the scope of protection of the present invention.

[0020] Example 1

[0021] refer to Figures 1-4 This embodiment provides a method for preparing artificial wetland filler made from recycled aggregate from construction waste modified with iron and manganese active interface, specifically including the following steps:

[0022] (1) Aggregate pretreatment

[0023] Waste concrete blocks are selected as raw materials. Wood chips, plastics, metal parts and other non-concrete impurities are removed. After being crushed by a jaw crusher and screened, aggregate particles with a particle size of 2-8mm are selected for use.

[0024] The screened aggregate particles were repeatedly rinsed with tap water to remove surface dust, mud, sand, and loose cement paste, and then rinsed once with deionized water. The aggregate was then placed in a 105℃ oven and dried to constant weight to obtain pretreated recycled construction waste aggregate.

[0025] (2) Pickling and activation

[0026] Weigh 1000g of pretreated recycled construction waste aggregate and add 10L of 1.0mol / L hydrochloric acid solution to completely submerge the aggregate. Soak at room temperature for 3 hours, stirring every 30 minutes during the soaking process to ensure that the hydrochloric acid solution fully contacts the surface and internal pores of the aggregate.

[0027] After pickling, the aggregate is removed, rinsed with deionized water until the pH of the rinsing solution is 6.8-7.2, and then dried in an oven at 105℃ for 6 hours to obtain acid-activated recycled aggregate from construction waste.

[0028] After pickling, the loose slurry and some carbonate deposits on the surface of the aggregate are removed, and some of the covered pores are exposed, making it easier for the subsequent alkaline solution to contact the pore walls on the surface of the aggregate.

[0029] (3) Alkali washing and hole enlargement

[0030] Acid-activated recycled aggregate from construction waste was added to a 1.5 mol / L sodium hydroxide solution, with an aggregate mass to sodium hydroxide solution volume ratio of 1 g: 8 mL. The mixture was then immersed in a 70°C constant temperature water bath for 4 hours, with intermittent stirring during the immersion process.

[0031] After alkaline washing, the aggregate is removed and rinsed with deionized water until the pH of the rinsing solution is 7.0-8.0. Then it is dried at 105℃ until there is no obvious moisture on the surface, thus obtaining acid-base coupled activated recycled aggregate from construction waste.

[0032] After alkaline washing, the surface roughness of the aggregate increases, and some of the small pores become interconnected, allowing the iron-manganese mixed salt solution to further contact the outer surface of the aggregate and the shallow pore walls.

[0033] (4) Iron-manganese composite oxide loading

[0034] A mixed salt solution of ferrous sulfate and manganese sulfate was prepared, wherein the molar ratio of iron to manganese was 3:1, and the total concentration of metal ions was 0.15 mol / L. Acid-base coupled activated recycled aggregate from construction waste was added to the iron-manganese mixed salt solution at a mass ratio of aggregate to mixed salt solution of 1 g: 6 mL, and impregnated for 5 hours.

[0035] After impregnation, a 1.0 mol / L sodium hydroxide solution was slowly added dropwise under stirring to adjust the pH of the system to 8.5–9.0, allowing the iron and manganese components to precipitate in situ on the outer surface of the aggregate and within the interconnected pores of the surface layer. After standing and aging for another 2 hours, the aggregate was filtered, and the resulting aggregate was quickly rinsed with a small amount of deionized water to remove unbound free salts.

[0036] During the aging process, the iron-manganese hydroxide precursor gradually adheres to the pore walls of the aggregate and the outer surface of the particles. Since the preceding acid and alkali washing processes have exposed some surface pores, the iron-manganese precursor, in addition to being distributed on the outer surface of the particles, can also penetrate into the shallow interconnected pores of the aggregate. Subsequent calcination transforms the precursor into iron-manganese composite oxides and improves its adhesion stability on the pore walls.

[0037] The loaded aggregate was dried in an oven at 105℃ for 8 hours, and then transferred to a muffle furnace and calcined at 350℃ for 2.5 hours. After calcination, it was naturally cooled to room temperature to obtain the iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler.

[0038] After the above treatment, the iron-manganese composite oxide mainly adheres to the outer surface of the aggregate and the interconnected pores of the surface layer, forming an active iron-manganese interface together with the rough pore walls formed after acid and alkali activation. The resulting filler retains the particle shape of the recycled aggregate, does not require additional granulation, and can be directly used as the main filler for constructed wetlands.

[0039] The packing material obtained in Example 1 was subjected to basic characterization, and the results are shown in Table 1.

[0040] Table 1. Characterization results of recycled aggregate from construction waste before and after modification BET specific surface area Approximately 3.8 m² / g Approximately 9.6 m² / g Kong Rong Approximately 0.018 cm³ / g Approximately 0.046 cm³ / g Fe content Low background content Approximately 18.4 mg / g Mn content Low background content Approximately 6.1 mg / g

[0041] Table 1 shows that after acid washing, alkali washing, and iron-manganese loading treatment, the BET specific surface area and pore volume of the filler increased, and the exposure degree of surface pores and water contact conditions of the aggregate were improved. Fe and Mn components were detected in the modified filler, with Fe content of approximately 18.4 mg / g and Mn content of approximately 6.1 mg / g, indicating that the iron-manganese components were loaded on the outer surface of the aggregate and in the surface interconnected pores, forming an iron-manganese active interface on the aggregate surface.

[0042] Example 2

[0043] This embodiment uses the iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler obtained in Example 1 to treat water bodies containing trichloroaniline.

[0044] A small vertical flow constructed wetland reaction column was constructed, with an inner diameter of 150 mm and a height of 1000 mm. The reaction column consisted of a supporting drainage layer, a modified filler body layer, and a water distribution layer, arranged sequentially from bottom to top.

[0045] The drainage layer consists of gravel with a particle size of 10-20 mm and a thickness of 10 cm; the modified filler body layer uses the iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler prepared in Example 1, with a filling thickness of 60 cm; and the water distribution layer uses clean gravel with a particle size of 5-10 mm and a thickness of 8 cm. An outlet is provided at the bottom of the reaction column, and a uniform water distribution device is provided at the top to ensure that the incoming water can enter the modified filler body layer relatively evenly.

[0046] The water to be treated was simulated triclosan-containing wastewater, with an initial triclosan concentration set at 0.5–20 μg / L and an influent pH controlled at 6.8–7.5. The influent entered the reaction column from top to bottom, with a hydraulic retention time of 8 hours. Before formally introducing the triclosan-containing water, it was continuously flushed with clean water for 24 hours, maintaining the same hydraulic load as subsequent operation stages. This pre-flushing process removed fine particles, free salts, and small amounts of unstable iron and manganese components from the packing layer. After the effluent became clear and the pH stabilized, the influent was switched to triclosan-containing water.

[0047] During operation, influent and effluent samples were collected every 24 hours. After filtration through a 0.45 μm filter membrane, the triclosan concentration was determined using high-performance liquid chromatography (HPLC). After 10 days of continuous operation, the system entered a stable phase. During this stable operation period, the average triclosan concentration in the influent was 10.0 μg / L, the average triclosan concentration in the effluent was 1.18 μg / L, and the average triclosan removal rate was 88.2%.

[0048] Simultaneously, the concentrations of Fe and Mn in the effluent were monitored during stable operation. The Fe concentration ranged from 0.021 to 0.046 mg / L, and the Mn concentration ranged from 0.012 to 0.035 mg / L, remaining at a low level overall. During operation, the effluent pH remained between 7.1 and 7.8, no significant blockage was observed in the reaction column, and the effluent flow rate showed minimal variation.

[0049] During stable operation, the concentration of triclosan in the effluent was significantly lower than that in the influent. After entering the modified packing layer with the water flow, triclosan can penetrate the interconnected pores on the surface of the aggregate and come into contact with the rough pore walls and the surface of the iron-manganese composite oxide. Simultaneous monitoring results showed that the concentrations of Fe and Mn in the effluent were at low levels, indicating that there was no significant and continuous loss of iron and manganese components under continuous water influent conditions.

[0050] Example 3

[0051] This embodiment is basically the same as Example 1, except that the acid washing, alkaline washing, and iron-manganese loading conditions are adjusted as follows:

[0052] The hydrochloric acid solution concentration was 0.8 mol / L, and the acid washing time was 4 h; the sodium hydroxide solution concentration was 1.2 mol / L, the alkaline washing temperature was 75℃, and the alkaline washing time was 4 h; the molar ratio of iron to manganese was 2.5:1, and the total concentration of metal ions was 0.12 mol / L; the calcination temperature was 330℃, and the calcination time was 3 h.

[0053] The iron-manganese active interface modified construction waste recycled aggregate filler prepared in this embodiment was used in a vertical flow constructed wetland reactor column. The thickness of the modified filler body layer was 50 cm, the hydraulic retention time was 10 h, and the influent triclosan concentration was 5.0 μg / L. After continuous and stable operation, the effluent triclosan concentration remained below 0.7 μg / L, with an average removal rate of 86.4%.

[0054] After the above parameters are adjusted, the packing material can still be used for triclosan water treatment, and the triclosan concentration in the effluent remains at a low level.

[0055] Example 4

[0056] This embodiment provides a composite flow constructed wetland operation mode suitable for deep purification of landscape water bodies or urban tailwater.

[0057] The constructed wetland pond is divided into a front water distribution zone, a middle modified filler zone, and a rear water collection zone. The middle modified filler zone consists of a gravel support layer, a layer of iron-manganese active interface modified construction waste recycled aggregate filler, and a surface planting layer, arranged from bottom to top. The iron-manganese active interface modified construction waste recycled aggregate filler layer is 70 cm thick, and the filler material used is the iron-manganese active interface modified construction waste recycled aggregate constructed wetland filler prepared in Example 1. The surface planting layer is planted with wetland plants, whose roots extend into the upper area of ​​the modified filler layer.

[0058] The triclosan-containing water enters the modified filler zone from the front-end distribution area and flows through the modified filler layer via a combination of horizontal subsurface flow and localized vertical seepage, with a hydraulic retention time of 10–12 hours. The influent triclosan concentration is 0.1–2.0 μg / L, which is considered a trace pollutant. After the system stabilizes, the average triclosan removal rate is approximately 85%.

[0059] Under the above operating conditions, the modified packing material can be used not only in small reaction columns but also in engineering wetland ponds. For low-concentration triclosan-contaminated water that continuously enters the wetland system, this packing material can participate in the purification process without additional aeration or continuous addition of chemicals.

[0060] Example 5

[0061] This embodiment uses real effluent as influent to investigate the removal effect of modified packing material on triclosan.

[0062] Secondary treated effluent from a wastewater treatment plant was used as the test sample. The sample was used directly after settling without additional adjustment of COD, nitrogen, phosphorus, and salt content. Triclosan standard solution was added to the sample to maintain the influent triclosan concentration between 1.0 and 2.0 μg / L. A vertical flow small-scale reaction column was constructed using the iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler prepared in Example 1. The main filler layer thickness was 60 cm, and the hydraulic retention time was 8 h.

[0063] After 15 days of continuous operation, influent and effluent samples were collected for testing. During the stable operation period, the average triclosan concentration in the influent was 1.53 μg / L, and the average triclosan concentration in the effluent was 0.24 μg / L, with an average removal rate of approximately 84.3%. Compared with simulated triclosan-containing wastewater, natural organic matter, suspended particles, and inorganic ions in the actual effluent occupied some adsorption sites, but the modified packing material still maintained a high triclosan removal efficiency.

[0064] During operation, the concentrations of Fe and Mn in the effluent were simultaneously monitored. The Fe concentration ranged from 0.018 to 0.052 mg / L, and the Mn concentration ranged from 0.015 to 0.041 mg / L. No significant loss of iron and manganese components was observed. Under these actual effluent conditions, the iron-manganese active interface modified packing material can still be used for triclosan deep purification treatment.

[0065] Example 6

[0066] This embodiment tests the continuous operation stability of the modified packing.

[0067] A vertical flow reaction column was constructed using the iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler prepared in Example 1. The thickness of the main filler layer was 60 cm. The influent triclosan concentration was controlled at approximately 10.0 μg / L, the hydraulic retention time was 8 h, and the system operated continuously for 90 days. During operation, the influent and effluent triclosan concentrations were measured every 5 days, and the effluent pH and Fe and Mn concentrations were recorded simultaneously.

[0068] On days 10, 30, 60, and 90 of operation, the average removal rates of triclosan were approximately 88.2%, 86.7%, 84.9%, and 83.6%, respectively, as shown in the following figures. Figure 4 As shown in the figure, during 90 days of continuous operation, the effluent pH remained between 7.0 and 7.9, the Fe concentration ranged from 0.019 to 0.064 mg / L, and the Mn concentration ranged from 0.013 to 0.049 mg / L. No significant caking or severe clogging occurred in the packing layer. The operational results indicate that the modified packing material maintained a relatively stable triclosan removal effect under continuous operation conditions, and no significant and continuous leaching of iron and manganese components was observed.

[0069] Comparative Example 1

[0070] This comparative example uses unmodified recycled construction waste aggregate as the artificial wetland filler. The aggregate source, particle size, reaction column structure, filling thickness, influent triclosan concentration, and hydraulic retention time are all the same as in Example 2.

[0071] After stable operation, the average concentration of triclosan in the influent was 10.0 μg / L, the average concentration of triclosan in the effluent was 6.75 μg / L, and the average removal rate of triclosan was 32.5%.

[0072] Compared to Example 2, the unmodified recycled construction waste aggregate showed a lower capacity for removing triclosan. The unmodified aggregate had more residual cement paste on its surface, limited pore connectivity, and insufficient effective surface area for triclosan adsorption, resulting in a still high concentration of triclosan in the effluent.

[0073] Comparative Example 2

[0074] This comparative example uses a single acid-washed modified recycled construction waste aggregate as the artificial wetland filler. The specific treatment method is as follows: the pretreated recycled construction waste aggregate is soaked in a 1.0 mol / L hydrochloric acid solution for 3 hours, rinsed until neutral, and dried. Subsequent alkaline washing for pore expansion and loading of iron-manganese composite oxides are not performed. Other wetland operating conditions are the same as in Example 2.

[0075] After stable operation, the average concentration of triclosan in the influent was 10.0 μg / L, the average concentration of triclosan in the effluent was 4.29 μg / L, and the average removal rate of triclosan was 57.1%.

[0076] After a single acid wash, the triclosan removal rate of the aggregate improved, but it was still lower than that in Example 2. The above results show that when only part of the surface slurry is removed, the removal of triclosan by the filler is still limited, and subsequent pore expansion and loading of iron and manganese active components are still necessary.

[0077] Comparative Example 3

[0078] This comparative example uses recycled construction waste aggregate activated by acid-base coupling but without iron-manganese loading as artificial wetland filler. The specific treatment method is as follows: acid washing activation and alkali washing pore-expansion treatment are completed according to the steps in Example 1. After rinsing and drying, it is directly used as artificial wetland filler without iron-manganese mixed salt impregnation, in-situ precipitation, or calcination. Other operating conditions are the same as in Example 2.

[0079] After stable operation, the average concentration of triclosan in the influent is 10.0 μg / L, the concentration of triclosan in the effluent is about 3.0 to 3.5 μg / L, and the triclosan removal rate is about 65% to 70%.

[0080] After acid-base coupling activation, the pore structure of the aggregate was improved, and the triclosan removal rate was higher than that of unmodified aggregate and single-acid-washed aggregate; however, without the loading of iron-manganese composite oxides, the surface active sites of the filler were still insufficient. It can be seen that acid-base coupling activation mainly improves the pore contact conditions, while iron-manganese loading further supplements the surface active sites, and the two together affect the removal efficiency of the filler for triclosan.

[0081] Comparative Examples 1-3 show that the unmodified recycled construction waste aggregate has limited ability to remove triclosan; after single acid washing, the surface condition of the aggregate is improved, but the pore connectivity and surface activity are still insufficient; after acid-base coupling activation, the triclosan removal rate is further improved, but without the loading of iron-manganese composite oxides, the surface of the filler still lacks a stable triclosan enrichment interface. Compared with the above comparative examples, Example 2 underwent both acid-base coupling activation and iron-manganese composite oxide loading treatment, thus exhibiting a higher triclosan removal rate.

[0082] Comparative Example 4

[0083] This comparative example compares commonly used constructed wetland fillers with the modified filler obtained in Example 1. Natural gravel, ceramsite, zeolite, and iron-manganese active interface modified recycled construction waste aggregate were selected as fillers, respectively. The particle size of the fillers was controlled within the range of 2-8 mm, the thickness of the main filler layer was 60 cm, the average concentration of triclosan in the influent was 10.0 μg / L, the hydraulic retention time was 8 h, and the other operating conditions were the same as in Example 2.

[0084] After stable operation, the average triclosan concentration in the effluent from the natural gravel group was approximately 7.2 μg / L, with an average removal rate of approximately 28%; the average triclosan concentration in the effluent from the ceramsite group was approximately 5.6 μg / L, with an average removal rate of approximately 44%; the average triclosan concentration in the effluent from the zeolite group was approximately 4.8 μg / L, with an average removal rate of approximately 52%; and the average triclosan concentration in the effluent from the modified packing group obtained in Example 1 was 1.18 μg / L, with an average removal rate of 88.2%.

[0085] Natural gravel, ceramsite, and zeolite have a certain retention or adsorption effect on triclosan, but their overall removal rate is lower than that of iron-manganese active interface modified construction waste recycled aggregate filler. After acid and alkali treatment, the pore connectivity of the modified filler is improved, and the iron-manganese composite oxide is loaded in the surface pores, which is conducive to increasing the contact between triclosan and the filler surface.

[0086] Comparative Example 5

[0087] This comparative example is used to compare the differences in triclosan removal between single-metal-loaded aggregates and iron-manganese composite-loaded aggregates. Single-iron oxide-loaded recycled construction waste aggregates, single-manganese oxide-loaded recycled construction waste aggregates, and the iron-manganese active interface-modified recycled construction waste aggregate obtained in Example 1 were prepared respectively. Except for the type of metal salt, the acid washing, alkali washing, impregnation, precipitation, drying, and calcination conditions were the same as in Example 1.

[0088] The three types of packing materials were used in vertical flow constructed wetland reaction columns. The thickness of the main packing layer was 60 cm, the average triclosan concentration in the influent was 10.0 μg / L, the hydraulic retention time was 8 h, and the remaining operating conditions were the same as in Example 2. After stable operation, the average triclosan concentration in the effluent from the single iron oxide-loaded aggregate group was approximately 2.7 μg / L, with an average removal rate of approximately 73%; the average triclosan concentration in the effluent from the single manganese oxide-loaded aggregate group was approximately 2.3 μg / L, with an average removal rate of approximately 77%; and the average triclosan concentration in the effluent from the iron-manganese active interface modified aggregate group was 1.18 μg / L, with an average removal rate of 88.2%.

[0089] Both iron oxide and manganese oxide loading can improve the removal efficiency of triclosan from recycled construction waste aggregates, but the removal rate is higher after iron-manganese composite loading. After iron-manganese composite loading, in addition to the improved pore contact conditions, an iron-manganese composite oxide interface is formed on the aggregate surface. Therefore, the triclosan effluent concentration is lower than that of the single iron oxide loading group and the single manganese oxide loading group.

[0090] Implementation effect analysis

[0091] The results of the examples and comparative examples show that the removal efficiency of triclosan by recycled aggregates from waste concrete is improved after acid washing, alkali washing, and loading with iron-manganese composite oxides. Acid washing primarily removes weakly bound slurry and carbonate blockages from the aggregate surface, exposing some covered pores. Alkali washing further improves the connectivity of surface pores, allowing the iron-manganese mixed salt solution to enter shallow pores. The iron-manganese components, after in-situ precipitation, aging, and calcination, are loaded onto the rough pore walls, forming an active iron-manganese interface. The interconnectedness of these processes results in a higher triclosan removal rate for the modified filler compared to unmodified aggregates, single-acid-washed aggregates, acid-alkali activated aggregates without iron-manganese loading, and commonly used gravel, ceramsite, and zeolite fillers.

[0092] After 90 days of continuous operation, the modified packing material maintained a relatively stable triclosan removal effect, and the concentrations of Fe and Mn in the effluent did not show a sustained increase. This result indicates that the iron and manganese components are not simply mixed into the wetland bed in easily leached powder form, but rather are loaded on the outer surface of the aggregate and the surface pore walls, participating in water purification. This packing material can be used for effluent from urban wastewater treatment plants, landscape water replenishment, and surface runoff treatment affected by domestic pollution sources. It also provides a wetland packing material application method for the resource utilization of waste concrete aggregate.

Claims

1. A type of artificial wetland filler made from recycled aggregate from construction waste modified with iron and manganese active interface, characterized in that, The filler is an artificial wetland functional filler formed by loading iron-manganese composite oxides on the outer surface of the aggregate and in the interconnected pores of the surface layer after acid-base coupling activation treatment, using recycled aggregate from waste concrete as the bearing matrix. The recycled aggregate from the waste concrete is obtained by crushing, screening and washing waste concrete, with a particle size of 2-8 mm. The acid-base coupling activation treatment includes a sequential acid washing activation treatment and an alkaline washing pore-expanding treatment. The acid washing activation treatment is used to remove weakly bonded cement paste, carbonate blockages and loose attachments on the surface of the aggregate, while the alkaline washing pore-expanding treatment is used to improve the surface roughness of the pore walls and the connectivity of the pores in the aggregate. The iron-manganese composite oxide is formed by iron salts and manganese salts on the outer surface and surface pores of recycled construction waste aggregate after acid-base coupling activation, through pH adjustment, in-situ precipitation, aging, drying and calcination. The iron-manganese composite oxide and the rough pore walls formed after acid-base coupling activation together constitute the iron-manganese active interface. When triclosan-containing water flows through the artificial wetland filler layer, triclosan enters the surface interconnecting pores and is enriched and fixed on the rough pore walls and the surface of the iron-manganese composite oxide.

2. The iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler according to claim 1, characterized in that, The recycled aggregate from construction waste undergoes pretreatment before acid washing and activation treatment, and the pretreatment includes: Waste concrete is crushed and screened to obtain aggregate particles of 2-8mm. Use clean water or deionized water to rinse the aggregate particles to remove surface dust, mud, sand and loose cement paste; The washed aggregate particles are dried to constant weight at 100-110℃ to obtain pretreated recycled aggregate from construction waste.

3. The artificial wetland filler made of recycled aggregate from iron-manganese active interface modified construction waste according to claim 1, characterized in that, The pickling and activation treatment is as follows: the pretreated recycled aggregate from construction waste is immersed in a 0.5-1.5 mol / L hydrochloric acid solution, and the immersion reaction is carried out at a mass ratio of aggregate to hydrochloric acid solution of 1 g: (5-15) mL for 2-4 hours. During the soaking process, intermittent or continuous stirring is performed. After acid washing, the solution is rinsed with deionized water until the pH of the rinsing solution is 6.5-7.5, and then dried.

4. The iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler according to claim 1, characterized in that, The alkaline washing and pore-expansion treatment is as follows: The acid-washed and activated recycled aggregate from construction waste is immersed in a 1.0–2.0 mol / L sodium hydroxide solution at a constant temperature of 60–80°C for 3–5 hours, with the aggregate mass to sodium hydroxide solution volume ratio being 1 g: (5–12) mL. After alkaline washing, the rinsing solution is rinsed until the pH of the rinsing solution is 7.0–8.0, and then dried at 100–110°C to obtain acid-base coupled activated recycled aggregate from construction waste.

5. The iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler according to claim 1, characterized in that, The iron salt is one or more of ferrous sulfate, ferrous chloride, ferric sulfate or ferric chloride, and the manganese salt is one or more of manganese sulfate, manganese chloride or manganese nitrate. The molar ratio of iron to manganese in the iron salt and manganese salt is 2:1 to 4:1, and the total concentration of metal ions in the mixed salt solution formed by the iron salt and manganese salt is 0.05 to 0.30 mol / L. The iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler has a BET specific surface area of ​​8.0-11.5 m² / g, a pore volume of 0.035-0.055 cm³ / g, an Fe content of 15-22 mg / g, and a Mn content of 4.5-8.0 mg / g.

6. A method for preparing an artificial wetland filler made of recycled aggregate from iron-manganese active interface modified as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. The waste concrete construction waste is crushed, screened, washed and dried to obtain pretreated recycled aggregate of construction waste with a particle size of 2-8mm. S2. Place the pretreated recycled aggregate from construction waste in a hydrochloric acid solution for acid washing and activation. After acid washing, rinse until near neutral and dry to obtain acid-activated recycled aggregate from construction waste. S3. Place the acid-activated recycled aggregate from construction waste in a sodium hydroxide solution for alkaline washing and pore expansion. After alkaline washing, rinse and dry to obtain acid-base coupled activated recycled aggregate from construction waste. S4. The acid-base coupled activated recycled aggregate from construction waste is immersed in a mixed iron-manganese salt solution, and the pH of the solution is adjusted to allow the iron-manganese components to undergo in-situ precipitation and loading on the outer surface of the aggregate and in the interconnected pores of the surface layer. S5. After loading, the aggregate is subjected to solid-liquid separation, drying and calcination, and after cooling, iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler is obtained.

7. The preparation method according to claim 6, characterized in that, In step S4, the pH of the iron-manganese mixed salt solution is adjusted to 8.0-10.0 using sodium hydroxide solution, sodium carbonate solution, or ammonia water, so that the iron-manganese components form an iron-manganese hydroxide precursor layer on the outer surface and in the surface interconnected pores of the acid-base coupled activated construction waste recycled aggregate. After adjusting the pH, continue to let it stand for 1-3 hours to allow the iron-manganese hydroxide precursor layer to adhere to the outer surface of the aggregate and the surface pore walls. In step S5, the drying temperature is 100-110℃, the drying time is 6-12h, the calcination temperature is 300-400℃, and the calcination time is 2-3h, so that the iron-manganese hydroxide precursor layer is transformed into the iron-manganese composite oxide active layer.

8. A method for removing triclosan from water using iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler as described in any one of claims 1 to 5, characterized in that, Includes the following steps: The iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler is filled into the artificial wetland reaction zone to form a modified filler layer; Before introducing the water containing triclosan into the water body to be treated, the modified packing layer is pre-rinsed with clean water so that fine particles, residual salts and a small amount of unstable attached iron and manganese components in the packing layer are discharged with the rinsing water. The water containing triclosan is introduced into the constructed wetland reaction zone, so that the water flows continuously or intermittently through the modified filler layer. As the water to be treated flows through the modified packing layer, triclosan enters the interconnected pores on the surface of the packing and is enriched and fixed on the rough pore walls and the surface of the iron-manganese composite oxide, thereby reducing the concentration of triclosan in the water.

9. The method according to claim 8, characterized in that, The modified filler layer has a filling thickness of 40-80 cm, a hydraulic retention time of 6-12 h, and a triclosan influent concentration of 0.1-50 μg / L in the water to be treated. The constructed wetland reaction zone is a vertical flow constructed wetland, a horizontal subsurface flow constructed wetland, or a combined flow constructed wetland, and the water to be treated flows through the modified filler layer in a top-down, bottom-up, or horizontal subsurface flow manner.

10. The method according to claim 8, characterized in that, The modified filler layer includes a water distribution layer, a modified filler body layer, and a supporting drainage layer arranged sequentially along the water flow direction; The modified filler body layer is filled with the iron-manganese active interface modified construction waste recycled aggregate artificial wetland filler, the water distribution layer is used to evenly distribute the water containing triclosan to be treated, and the supporting drainage layer is used to support the modified filler body layer and collect the treated effluent. The volume of the iron-manganese active interface modified recycled aggregate from construction waste in the modified filler main layer accounts for 70% to 100% of the total volume of the modified filler main layer.

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