Electrochemical oxidation of PFOA and PFOS in concentrated waste streams

The electrochemical oxidation (EO) of environmentally persistent perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) with a Magnéli phase Ti₄O₇ electrode was investigated in this study. After 3 hours (hr) of electrolysis, 96.0 percent of PFOA (10 milligrams per liter [mg/L] in 100 milliliters [mL] 100 millimolar [mM] Na₂SO₄ solution) was removed following pseudo first‐order kinetics (k = 0.0226 per minute [min]) with the degradation half‐life of 30.7 min. Under the same treatment conditions, PFOS (10 mg/L in 100 mL 100 mM Na₂SO₄ solution) removal reached 98.9 percent with a pseudo first‐order degradation rate constant of 0.0491/min and the half‐life of 14.1 min. Although, the degradation of PFOA was slower than PFOS, when subjected to EO treatment in separate solutions, PFOA appeared to degrade faster than PFOS when both are present in the same solution, indicating possible competition between PFOA and PFOS during Ti₄O₇ anode‐based EO treatment with PFOA having the competitive advantage. Moreover, the EO treatment was applied to degrade highly concentrated PFOA (100.5 mg/L) and PFOS (68.6 mg/L) in ion‐exchange resin regenerant (still bottom) with high organic carbon content (15,800 mg/L). After 17‐hr electrolysis, the total removal of PFOA and PFOS was 77.2 and 96.5 percent, respectively, and the fluoride concentration increased from 0.84 mg/L to 836 mg/L. Also, the dark brown color of the original solution gradually faded during EO treatment. In another test using still bottom samples with lower total organic carbon (9,880 mg/L), the PFOA (15.5 mg/L) and PFOS (25.5 mg/L) concentrations were reduced to levels below the limits of quantification after 16‐hr treatment. In addition, the performance of EO treatment using different batch reactor setups was compared in this study, including one‐sided (one anode:one cathode) and two‐sided (one anode:two cathodes) setups. The two‐sided reactor configuration significantly enhanced the degradation efficiency, likely due to the larger anode area available for reactions.     

Physico-chemical and biological treatment of MSW landfill leachate

This paper analyses the evolution of the physico-chemical characteristics of the leachate from the Central Landfill of Asturias (Spain), which has been operating since 1986, as well as different treatment options. The organic pollutant load of the leachate, expressed as chemical oxygen demand (COD), reached maximum values during the first year of operation of the landfill (around 80,000 mg/L), gradually decreasing over subsequent years to less than 5000 mg/L. The concentration of ammonium, however, has not decreased, presenting values of up to 2000 mg/L. When feasible, recirculation can greatly decrease the organic matter content of the leachate to values of 1500–1600 mg COD/L. Applying anaerobic treatment to leachates with a COD between 11,000 and 16,000 mg/L, removal efficiencies of 80–88% were obtained for organic loading rates of 7 kg COD/m³ d. For leachates with lower COD (4000–6000 mg/L), the efficiency decreased to around 60% for organic loading rates of 1 kg COD/m³ d.Applying coagulation–flocculation with iron trichloride or with aluminium polychloride, it was possible to reduce the non-biodegradable organic matter by 73–62% when treating old landfill leachate (COD: 4800 mg/L, BOD₅: 670 mg/L), also reducing turbidity and colour by more than 97%. It is likewise possible to reduce the non-biodegradable organic matter that remains after biological treatment by adsorption with activated carbon, although adsorption capacities are usually low (from 15 to 150 mg COD/g adsorbent). As regards ammonium nitrogen, this can be reduced to final effluent values of 5 mg/L by means of nitrification/denitrification and to values of 126 mg/L by stripping at pH 12 and 48 h of stirring.     

Landfill Leachate Ecotoxicity Experiments using Lemna minor

The effects of varying concentrations of landfill leachate on the growth, frond area, chlorophyll content and fluorescence of four strains of Lemna minor were assessed. Growth fluorescence and frond chlorophyll content decreased after seven days exposure to leachate, although responses differed between the strains and end parameters. A L. minor bioassay was used to assess leachate toxicity and the effectiveness of a constructed wetland treatment system and pre-treatment aeration and settlement in reducing toxicity. Pre-treatments were found to significantly reduce toxicity, so their incorporation in any treatment system may increase pollutant stripping.     

Heterotrophic Biological Denitrification Using Microbial Cellulose as Carbon Source

The objective of this study was to investigate the feasibility of using a microbial biopolymer produced by Acetobacter xylinum as a carbon source for heterotrophic biological denitrification. The denitrification rate, COD availability and nitrite concentration were response parameters. Under the experimental conditions, a denitrification rate of about 0.74 kg NO₃ ⁻N/m³d at 6 h retention time was achieved with microbial cellulose (MC). The reactor effluent contained significantly COD concentrations (20–86 mg/L) so it was not carbon limited, and was receiving enough carbon to facilitate the denitrification process. The maximum nitrite concentration in the effluent was found to be 0.4 mg/L. However, decreasing the retention time to 3 h significantly reduced the efficiency. It can be concluded that the MC is a suitable carbon source for nitrate removal in a heterotrophic biological denitrification process.     

Anaerobic treatment of effluents from an industrial polymers synthesis plant

The feasibility of the anaerobic treatment of an industrial polymer synthesis plant effluent was evaluated. The composition of the wastewater includes acrylates, styrene, detergents, a minor amount of silicates and a significant amount of ferric chloride. The average chemical oxygen demand (COD) corresponding is about 2000 mg/l. The anaerobic biodegradability of the effluent is shown and the toxicity effect on the populations of anaerobic bacteria is evaluated. The results of the anaerobic biodegradation assays show that 62% of the wastewater compounds, measured as COD, could be consumed. An upflow anaerobic sludge blanket (UASB) reactor was used in the evaluation, it has a diameter–height ratio of 1:7, and 4-liter volume. The inoculum was obtained from a UASB pilot plant that treats brewery wastewaters. At the beginning of the operation, the biomass showed an anaerobic activity of 0.58 gCOD/(gVSS×d), it decreased only 2.5% in the subsequent 4 months. After 35 days of continuous operation, the reactor was operated at different steady states for 140 days. The COD was maintained at 2200 mg/l in the feed. The results were: organic loading rate (OLR): 4.3 kg COD/(m³×d), hydraulic retention time: 12 h, superficial velocity: 1 m/h, average biogas productivity: 290 L CH₄/kg COD fed, biogas composition: 70–75% methane and a COD removal percentage >75%. ©     

Combined processes of two-stage Fenton-biological anaerobic filter–biological aerated filter for advanced treatment of landfill leachate

There are numerous non-biodegradable organic materials in the mature landfill leachate. To meet the new discharge standard of China, additional advanced treatment is needed for the effluent from the biological treatment processes of leachate. In this study, a combined process including two stages of “Fenton-biological anaerobic filter (BANF)–biological aerated filter (BAF)” was evaluated to address the advanced treatment need. The Fenton oxidation was applied to reduce chemical oxygen demand (COD) and enhance biodegradability of refractory organics, and the BANF–BAF process was then applied to remove the total nitrogen (TN). The treatment achieved effluent concentrations of COD < 70 mg/L, TN < 40 mg/L and NH₃–N < 10 mg/L. The removal efficiency of COD and TN were 96.1% and 95.9%, respectively. The effluent quality met the new discharge standard for Pollution Control on the Landfill Site of Municipal Solid of PR China (GB16889-2008). The operation cost of these processes was about 36.1 CHY/t (5.70 USD/t).     

二氧化氯催化氧化—曝气生物滤池法深度处理造纸废水

采用二氧化氯催化氧化法—BAF法深度处理造纸废水，实验结果表明:在二氧化氯加入量为150mg/L，催化氧化时间为40min时，可生化性BOD5/COD最高达到0.316;二氧化氯氧化后出水经曝气生物滤池深度处理后，BOD5低于20mg/L，COD低于90mg/L，TSS低于30mg/L，处理后水质完全达到国家新的排放标准(GB3544—2008)。     

Chemical oxidation using stabilized hydrogen peroxide in high temperature,saline groundwater impacted with hydrocarbons and MTBE

In situ chemical oxidation (ISCO) of petroleum hydrocarbons (PHCs) within groundwater is considered a proven approach to addressing PHC‐impacted groundwater in nonsaline environments. One of the most common oxidants used for oxidation of PHCs in groundwater is hydrogen peroxide (H₂O₂). Due to its highly reactive nature, H₂O₂ is often stabilized to aid in increasing its reactivity lifespan. Limited research and application of ISCO has been completed in warm, saline groundwater environments. Furthermore, even fewer studies have been completed in these environments for ISCO using stabilized H₂O₂. In this research, stabilized H₂O₂ was examined to determine its effectiveness in the treatment of PHCs and the additive methyl tert‐butyl ether (MTBE). Three stabilizers (citrate, phytate, silica [SiO₂]) were tested to determine if the stabilizers could enhance and extend the treatment life of H₂O₂ within saline groundwater. To determine the effect of salinity on the three stabilizers, groundwater and aquifer samples were collected from two saline locations that had different salinity (total dissolved solids of about 7,000 mg/L and 18,000 mg/L). Specific target chemicals for treatment were water soluble, mobile components of gasoline including benzene, toluene, ethylbenzene, xylenes, (BTEX) and MTBE. Previous studies using unactivated persulfate indicated that the PHCs within the groundwater could be oxidized, however, only limited oxidation of the MTBE could be affected. The results of the laboratory tests indicated that greater than 95 percent of the target hydrocarbons were removed within 7 days of treatment. Microcosms with citrate‐stabilized H₂O₂ demonstrated a significantly faster and greater decline with most hydrocarbon concentrations reaching < 5 μg/L. The exceptions were ethylbenzene and m‐xylene, which were slightly decreased to about 30 and 20 μg/L, respectively. Initial mean concentrations of the BTEX compounds within the citrate‐stabilized microcosms were 10,554 μg/L, 9,318 μg/L, 6,859 μg/L, and 14,435 μg/L, respectively. The silicate‐stabilized H₂O₂ microcosms showed no significant benefit over the unstabilized control microcosms. The better performance of citrate‐stabilized microcosms was confirmed by increasing δ13C values of remaining hydrocarbons. MTBE declined from > 400 mg/L to < 100 mg/L in all microcosms, again with the best removal (> 90 percent) being measured in the citrate‐stabilized microcosms. Unfortunately, H₂O₂ oxidation in the microcosms also resulted in production of up to 40 mg/L TBA or approximately 10 percent of the MTBE oxidized.     

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.     

UASB-SBR-絮凝工艺处理地沟油制生物柴油废水

采用UASB-SBR-絮凝工艺处理地沟油制生物柴油废水，考察了各个阶段的废水处理效果。实验结果表明：UASB稳定运行阶段进水COD约为15000mg/L时，COD去除率约为87%，出水COD在2500mg/L以下，出水挥发性脂肪酸（VFA）浓度为4~6mmol/L，最佳容积负荷为15.0kg/（m3·d）；采用SBR处理UASB出水，当容积负荷为1.5kg/（m3·d）时，出水COD在200mg/L以下，COD去除率在83%以上，ρ（NH₃-N）在5mg/L以下，TP约为25mg/L。向SBR出水中加入质量分数为5%的聚合氯化铝进行化学除磷，加入量为5mL/L，处理后废水TP为4~6mg/L。处理后废水的COD，ρ（NH₃-N），TP均达到CJ343-2010《污水排入城市下水道水质标准》的A类要求。     

Stabilization of heavy metals in MSWI fly ash using silica fume

The objective of this work was to investigate the feasibility and effectiveness of silica fume on stabilizing heavy metals in municipal solid waste incineration (MSWI) fly ash. In addition to compressive strength measurements, hydrated pastes were characterized by X-ray diffraction (XRD), thermal-analyses (DTA/TG), and MAS NMR (²⁷Al and ²⁹Si) techniques. It was found that silica fume additions could effectively reduce the leaching of toxic heavy metals. At the addition of 20% silica fume, leaching concentrations for Cu, Pb and Zn of the hydrated paste cured for 7 days decreased from 0.32 mg/L to 0.05 mg/L, 40.99 mg/L to 4.40 mg/L, and 6.96 mg/L to 0.21 mg/L compared with the MSWI fly ash. After curing for 135 days, Cd and Pb in the leachates were not detected, while Cu and Zn concentrations decreased to 0.02 mg/L and 0.03 mg/L. The speciation of Pb and Cd by the modified version of the European Community Bureau of Reference (BCR) extractions showed that these metals converted into more stable state in hydrated pastes of MSWI fly ash in the presence of silica fume. Although exchangeable and weak-acid soluble fractions of Cu and Zn increased with hydration time, silica fume addition of 10% can satisfy the requirement of detoxification for heavy metals investigated in terms of the identification standard of hazardous waste of China.     

Membrane bioreactor technology: A novel approach to the treatment of compost leachate

Compost leachate forms during the composting process of organic material. It is rich in oxidizable organics, ammonia and metals, which pose a risk to the environment if released without proper treatment. An innovative method based on the membrane bioreactor (MBR) technology was developed to treat compost leachate over 39 days. Water quality parameters, such as pH, dissolved oxygen, ammonia, nitrate, nitrite and chemical oxygen demand (COD) were measured daily. Concentrations of caffeine and metals were measured over the course of the experiment using gas chromatography – mass spectrometry (GC/MS) and inductively coupled plasma – mass spectrometry (ICP–MS) respectively. A decrease of more than 99% was achieved for a COD of 116 g/L in the initial leachate. Ammonia was decreased from 2720 mg/L to 0.046 mg/L, while the nitrate concentration in the effluent rose to 710 mg/L. The bacteria in the MBR system adjusted to the presence of the leachate, and increased 4 orders of magnitude. Heavy metals were removed by at least 82.7% except copper. These successful results demonstrated the membrane bioreactor technology is feasible, efficient method for the treatment of compost leachate.     

微电解—Fenton氧化—絮凝组合工艺处理油田压裂废水

采用微电解—Fenton氧化—絮凝组合工艺处理油田压裂废水,优化了工艺条件。实验结果表明：最佳工艺条件为初始废水pH 3.0、铁屑加入量1.5 g/L（铁屑与活性炭的质量比1∶1）、微电解时间80 min、Fenton氧化时间120 min、H₂O₂加入量940 mg/L,阳离子聚丙烯酰胺加入量120 mg/L;在最佳工艺条件下处理废水后,COD由3 116.0 mg/L降至681.3 mg/L,总COD去除率达78.1%,3个工段的COD去除率依次为33.1%,37.9%,7.1%,出水水质满足现场回注标准（SY/T 5329—2012《碎屑岩油藏注水水质推荐指标及分析方法》）;该组合工艺对废水的处理效果远优于单独微电解、Fenton氧化或絮凝工艺,且方法简单易行、药剂利用率高。     

Emission of volatile sulfur compounds during composting of municipal solid waste (MSW)

Volatile sulfur compounds (VSCs) are the main source for malodor from composting plants. In this study, the VSCs generated from composting of 15–80 mm municipal solid waste (T0), kitchen waste (T1) and kitchen waste mixed dry cornstalks (T2) were measured in 60 L reactors with forced aeration for a period of 30 days. The VSCs detected in all treatments were hydrogen sulfide (H₂S), methyl mercaptan (MM), dimethyl sulfide (DMS), carbon bisulfide (CS₂) and dimethyl disulfide (DMDS). Over 90% of the VSCs emissions occurred during the first 15 days, and reached their peak values at days 4–7. The emission profiles of five VSCs species were significantly correlated with internal materials temperature and outlet O₂ concentration (p < 0.05). Total emissions of the VSCs were 216.1, 379.3 and 126.0 mg kg^?1 (dry matter) for T0, T1 and T2, respectively. Among the five VSCs, H₂S was the most abundant compound with 39.0–43.0% of total VSCs released. Composting of kitchen waste from separate collection posed a negative influence on the VSC and leachate production because of its high moisture content. An addition of dry cornstalks at a mixing ratio of 4:1 (wet weight) could significantly reduce the VSCs emissions and avoid leachate. Compared to pure kitchen waste, VSCs were reduced 66.8%.     

分子筛催化剂生产废水的生物处理

采用氨化—硝化—反硝化三段联合生物工艺处理分子筛催化剂生产过程中产生的含有机胺废水。实验结果表明：在氨化过程中，当进水COD稳定为1 200~1 600 mg/L时，出水COD低于300 mg/L，COD去除率稳定在80%左右，当进水ρ（有机氮）为100~160 mg/L时，出水ρ（有机氮）均低于30 mg/L，有机氮去除率大于80%，在整个氨化过程中，出水ρ（氨氮）较进水ρ（氨氮）提高了35~200 mg/L;硝化过程中，当进水ρ（氨氮）小于等于300 mg/L时，出水ρ（氨氮）最终稳定在15 mg/L以内，氨氮去除率大于90%;在反硝化过程中，亚硝酸盐氮去除率基本稳定在98%以上，最终出水COD低于80 mg/L，出水ρ（总氮）低于25 mg/L。     

Poly(hydroxyalkanoate) Biosynthesis from Crude Alaskan Pollock (Theragra chalcogramma) Oil

Six strains of Pseudomonas were tested for their abilities to synthesize poly(hydroxyalkanoate) (PHA) polymers from crude Pollock oil, a large volume byproduct of the Alaskan fishing industry. All six strains were found to produce PHA polymers from hydrolyzed Pollock oil with productivities (P; the percent of the cell mass that is polymer) ranging from 6 to 53% of the cell dry weight (CDW). Two strains, P. oleovorans NRRL B-778 (P = 27%) and P. oleovorans NRRL B-14682 (P = 6%), synthesized poly(3-hydroxybutyrate) (PHB) with number average molecular weights (M_n) of 206,000 g/mol and 195,000 g/mol, respectively. Four strains, P. oleovorans NRRL B-14683 (P = 52%), P. resinovorans NRRL B-2649 (P = 53%), P. corrugata 388 (P = 43%), and P. putida KT2442 (P = 39%), synthesized medium-chain-length PHA (mcl-PHA) polymers with M_n values ranging from 84,000 g/mol to 153,000 g/mol. All mcl-PHA polymers were primarily composed of 3-hydroxyoctanoic acid (C_8:0) and 3-hydroxydecanoic acid (C_10:0) amounting to at least 75% of the total monomers present. Unsaturated monomers were also present in the mcl-PHA polymers at concentrations between 13% and 16%, providing loci for polymer derivatization and/or crosslinking. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.     

Comparison of different liquid anaerobic digestion effluents as inocula and nitrogen sources for solid-state batch anaerobic digestion of corn stover

Effluents from three liquid anaerobic digesters, fed with municipal sewage sludge, food waste, or dairy waste, were evaluated as inocula and nitrogen sources for solid-state batch anaerobic digestion of corn stover in mesophilic reactors. Three feedstock-to-effluent (F/E) ratios (i.e., 2, 4, and 6) were tested for each effluent. At an F/E ratio of 2, the reactor inoculated by dairy waste effluent achieved the highest methane yield of 238.5 L/kgVS_feed, while at an F/E ratio of 4, the reactor inoculated by food waste effluent achieved the highest methane yield of 199.6 L/kgVS_feed. The microbial population and chemical composition of the three effluents were substantially different. Food waste effluent had the largest population of acetoclastic methanogens, while dairy waste effluent had the largest populations of cellulolytic and xylanolytic bacteria. Dairy waste also had the highest C/N ratio of 8.5 and the highest alkalinity of 19.3 g CaCO₃/kg. The performance of solid-state batch anaerobic digestion reactors was closely related to the microbial status in the liquid anaerobic digestion effluents.     

The in situ treatment of TCE and PFAS in groundwater within a silty sand aquifer

Chlorinated ethenes such as trichloroethene (TCE), cis‐1,2‐dichloroethene (cis‐1,2‐DCE), and vinyl chloride along with per‐ and polyfluoroalkyl substances (PFAS) have been identified as chemicals of concern in groundwater; with many of the compounds being confirmed as being carcinogens or suspected carcinogens. While there are a variety of demonstrated in‐situ technologies for the treatment of chlorinated ethenes, there are limited technologies available to treat PFAS in groundwater. At a former industrial site shallow groundwater was impacted with TCE, cis‐1,2‐DCE, and vinyl chloride at concentrations up to 985, 258, and 54 µg/L, respectively. The groundwater also contained maximum concentrations of the following PFAS: 12,800 ng/L of perfluoropentanoic acid, 3,240 ng/L of perfluorohexanoic acid, 795 ng/L of perfluorobutanoic acid, 950 ng/L of perfluorooctanoic acid, and 2,140 ng/L of perfluorooctanesulfonic acid. Using a combination of adsorption, biotic, and abiotic degradation in situ remedial approaches, the chemicals of concern were targeted for removal from the groundwater with adsorption being utilized for PFAS whereas adsorption, chemical reduction, and anaerobic biodegradation were used for the chlorinated ethenes. Sampling of the groundwater over a 24‐month period indicated that the detected PFAS were treated to either their detection, or below the analytical detection limit over the monitoring period. Postinjection results for TCE, cis‐1,2‐DCE, and vinyl chloride indicated that the concentrations of the three compounds decreased by an order of magnitude within 4 months of injection, with TCE decreasing to below the analytical detection limit over the 24‐month monitoring period. Cis‐1,2‐DCE, and vinyl chloride concentrations decreased by over 99% within 8 months of injections, remaining at or below these concentrations during the 24‐month monitoring period. Analyses of Dehalococcoides, ethene, and acetylene over time suggest that microbiological and reductive dechlorination were occurring in conjunction with adsorption to attenuate the chlorinated ethenes and PFAS within the aquifer. Analysis of soil cores collected pre‐ and post‐injection, indicated that the distribution of the colloidal activated carbon was influenced by small scale heterogeneities within the aquifer. However, all aquifer samples collected within the targeted injection zone contained total organic carbon at concentrations at least one order of magnitude greater than the preinjection total organic carbon concentrations.     

Modeling remediation time using natural attenuation at a dry‐cleaner site

Contaminants from dry‐cleaning sites, primarily tetrachloroethene (PCE), trichloroethene (TCE), cis‐dichloroethene (cis‐DCE), and vinyl chloride (VC), have become a major concern because of the limited funds and regulatory programs to address them. Thus, natural attenuation and its effectiveness for these sites needs to be evaluated as it might provide a less costly alternative to other remediation methods. In this research, data from a site in Texas were analyzed and modeled using the Biochlor analytical model to evaluate remediation times using natural attenuation. It was determined that while biodegradation and source decay were occurring at the site, the resulting attenuation rates were not adequate to achieve cleanup in a reasonable time frame without additional source remediation or control strategies. Cleanup times exceeded 100 years for all constituents at the site boundary and 800 years at the source for PCE, assuming cleanup levels of 0.005 mg/L for PCE and TCE and 0.07 mg/L and 0.002 mg/L for cis‐DCE and VC, respectively. © 2005 Wiley Periodicals, Inc.     

强化混凝法处理煤气冷凝水

以包头钢铁(集团)有限责任公司高炉煤气冷凝水为处理对象，采用强化混凝法进行静态混凝沉淀对比实验。实验结果表明，当聚合氯化铝加入量为20mg/L、高分子纳米除氯剂加入量为2.0mL/L时，处理后出水SS小于10mg/L，浊度小于10NTU，氯离子去除率在80%以上，而且对废水中的其他离子也有一定的去除效果，出水水质基本接近工业冷却循环水回用指标。