| 英文摘要 |
This study was carried out in order to comply with the Environmental Protection Administration’s initiatives in encouraging innovation or research ＆ development in waste recycling treatments. The focus is on how to increase recycling and reuse of waste paper containers and secondary fiber yield from such sources. In addition, pollutant discharging quantities during the treatments will be evaluated so as to be undertaken as a project in evaluating potential of increasing waste paper container recovery rate and fiber yields. Domestic consumption of paper meal boxes exceeded 5 billion units, resulting in annual wasting of 75,000 ton of paper resource. However, because these waste paper meal boxes must have grease- and water-proof properties, wet-strength agents are added during the paperboard forming process, and on top special treatment of PE film lamination need to be done. As a result, they are not easily disintegrated during recycling, and the wastewater often contains high amounts of BOD, causing increases to the handling costs of paper mills.
In order to increase the recovery rate of such waste paper containers, hindrances such as secondary fiber yield must be increased, BOD loading of effluents must be resolved, and product flux issue etc., then paper mills perhaps will be willing to handle the raw materials. In the study the Dept. of Environmental Engineering, Dayeh University and Long Cheng Paper inc. form a team to mutually undertaking review of pertinent roadblocks of fiber yield enhancement technologies, BOD loading of the wastewater treatment system, and end-product marketing. Full considerations of technological developments and marketing paths integration are carried out in a bid to effectively increase wastepaper container recovery, reduce their environmental impact, and to achieve the goal of enhanced resource reuses.
Therefore, the objectives of this project are to effectively increase the recovered quantities of wastepaper containers, and to solve the problem of BOD loading to the wastepaper treatment system etc. Hence, the research methodology involved collaboration of the Dept. of Environmental Engineering, Dayeh University; and Long Cheng Paper Inc. so as to successfully complete the project. The laboratory framework involved operating the treatments of wastepaper meal boxes; the salient work items included collection of pertinent references, and establish an experimental design based on the literature information and conditions suitable for the mill site operations. Then experiments were carried out using the collected and treated samples following the design scheme. The data obtained were then analyzed statistically based on the experimental design. The feedbacks from the initial set of experiment were then incorporated into subsequent experiments. Finally, the data were integrated to establish a recommended pilot mill operational reference. The post-laboratory pilot study was the main focus of the project. The pulp disintegration efficiency based on the laboratory study was scaled-up in the pilot experiment. Not only the yield rates were estimated, the physico-chemical and biological reactions occurring during the repulping processions were engaged to evaluate the process efficiency and pollution loading indicators. This part of data could serve an important full-size mill operational reference.
The objectives of the project at various phases included that for laboratory-scale experiments (fiber yield enhancement); because of the high sizing degree, high wet strength, PE lamination properties, the present mill fiber recovery rate was only ca. 40%. Often large amounts of fibers are retained with the rejected PE films, leading to inefficient recycling and poor reuse. Therefore, the project intends to develop chemical aids for pulp disintegration and optimization of repulping process, so as to increase the fiber recovery rate from 40% to more than 70%.
Pilot-scale experiments and effluent quality simulation (investigation of the wastewater treatment plant effluent loading problem): The project carried out a pilot-scale experimental set, and the lab water quality results were used to estimate effluent treatment conditions. Optimization of the pilot-scale experimental conditions would be deployed to actual mill operations in a cooperating mill, and upon further optimization, to operate accordingly. Dayeh University shall assist in sorting operational conditions and analyze data. Hence, in the study, the pilot-scale experiment shall provide water quality data for predicting actual mill effluent quality variations and provide reference for subsequent applications.
According to the “Subsidy rates of reclamation and disposal of designated recyclable containers,”which was promulgated by the Environmental Protection Administration in Aug. 18, 2011, wastepaper containers are defined as 3 groups of aluminum-laminated packages, air-tight or liquid-tight paper containers (Tetrapak); other paper containers; and containers of plant fibers (meal boxes). And according to the “audited and certified waste objects and containers recycling quantity statistics”, in 2011, waste aluminum-laminated packages was 9,389.4 ton/year; waste paper containers was 9,612.8 ton/year (of these waste paper meal boxes was 7,274.3 ton/year; waste paper utensils 2,338.5 ton/year). For many years, recovery rate of waste paper meal boxes was only about 25%. At present, domestic import base paper about 1,000 ton/month, of which 60% was used for making paper utensils, and 40% for making meal boxes.
Based on the above discussion, in order to effectively increase the wastepaper container recycling amounts, fiber yield must be increased, wastewater BOD loading must be solved, and marketing channel blockages must be removed. Only afterward, paper mill will have incentive to handle the materials. This project combines the resources of Dayeh University and Long Cheng Paper Inc. to undertake comprehensive technological develop- ment and integration of marketing channels so as to provide solutions to the aforementioned issues. We hope that a wastepaper container reutilization supply chain can be constructed which effectively increase wastepaper container recovery rate and reduce their environmental loading as well as attaining the goal of increase resource reuses.
Summarizing the above, the probable causes of low wastepaper containers recovery rate are as follows:
1) Inconvenient in recycling handling.
2) Method of calculating urban wastes disposal costs can not reflect the benefit of recycling.
3) Users have no feeling of direct paying for the recycling
4) Exclusive effects of other environmental actions
5) Wastepaper containers are difficult to process
6) Drawback of secondary pollution
7) Subsidy at present presented insufficient incentives
In the lab-scale experiments, the samples used were general commercial paper meal boxes. Before repulping, large amount of meal boxes were cut into 1 x 1 inch square for a total weight of about 10 kg. The pieces were homogenized and randomly selected for experiment, and avoiding error from different batches of cutting. After consulting literature on experimental design, repulping experiments were carried out. With regard to variables of repulping heating temperature, heating time, and repulping time, a 23 factor design was setup to provide understandings to the effects of these variables on repulping. The targeted fraction to be collected was passing a 14 mesh screen; which has pore diameter of ca. 1.40 mm. Factorial analysis of the heating temperature, heating time, and repulping time main effects and their interactions were carried out. Pulp recovery was found to be affected by heating temperature and repulping time. Heat time and the interactions among the variables were not significant. The results from the experimental design indicated that using high energy consumption repulping process (such as high heating temperature and long repulping time) in the first phase (Phase I) could lead to ca. 30% gain in fiber recovery. The Phase II and III of the experimental designs used lower energy consumption conditions to repulp. In the Phase II, pH of the repulping system was modulated individually to 3, 7, and 11 and the stock was heated to 90℃ and repulped 30 min. In the series, the best fiber yield was about 62% even with addition of chemicals. The Phase III enzymatic treatment conditions was milder than the chemical ones, at doses of 1 to 5%, operating temperature of 45-65℃, and pH 6-8. Reaction time was longer, and required 1-16 h. The experimental design added enzyme preparation at 10-15% to dry pulp, which converted to 1.0-1.5% enzyme doses. The operational temperature was set at 50℃, and 3 kinds of enzymes were tested. The enzyme A at 15% dose resulted in fiber yield of 63.35%; 10% dose of enzyme B achieved a fiber yield of 63.44%; and 15% of enzyme C resulted in a maximum fiber yield of 57.55%.
In the pilot-scale experiments, the lab results were used as a foundation and the most optimal repulping operational conditions were used in the process. The design variables were pulp consistency 1.0 and 2.0%; heated to 50℃ and 90℃ for 1 and 2 h, then proceed to low hydraulic type pulper to disintegrate for 15 min. Upon completion of repulping, a 14 mesh screen was used to collect passing fibers for yield calculation. In the meantime, filtrate water samples were collected to examine the effects of chemicals added on the wet strength agent debonding reaction and drainage. Effluent SS, COD, and BOD were tested.
In the first step (step I), in order to understand the effects of heating temperature (50, 90℃), and heating time (1.0, 2.0 h) on the fiber yield. After heating to 90℃ for 2 h, the pass 14 mesh pulp yield could reach 62%; at 90℃ and 1 h, pulp yield was 55%. These were based on the entire paper meal boxes. If the mass of PE film was deducted, then fiber yield reached 73% and 65%, respectively for the above conditions. In step 2, we examined the effect of pulp consistency at different heating temperature and pulping time on the fiber yield. For both 1% and 2% consistency the fiber yield was 555. In step 3, we kept the heating temperature variable range, and examined the effect of pulp pH (4, 7, 11) on the fiber yield At 1% consistency, adding pH modulating chemical could increase fiber yield to a maximum of 66%; with 66%, 55%, and 64% obtained for pH 4, 7, and 11, respectively. If mass of PE film were deducted, then the corresponding yields were 78%, 64%, and 75%, respectively. This achieved the goal we set out to attain. In step 4, various enzymes were applied to see their effect on the fiber yield. The results indicated a yield of ca. 27% which fall short of good efficacy. Thus, the subsequent experiments shall mainly based on manipulation of the chemical methods.
The design of our experiments shall use the pilot-scale results as the basis for actual mill operation trials. However, although the cooperating mill did handle Tetrapaks during the interim of the study, paper meal boxes, in recycled wastepaper were insufficient due to subsidy rate adjustment and recycling policy preference. Therefore, we could only conduct review of the cooperating mill’s pulping and recycling process in a bid to setup a guideline for handling wastepaper based such products in the future. At the surveying date, the mill uses a pulp consistency of 3.2% and a pulping temperature of 50℃.
In the part of effluent quality analysis, the project conducted treatments using the pilot-scale effluent. Regarding SS, COD, and BOD were analyzed and compared with the cooperating mill effluent status. At present, the mill treats 6000 ton of effluent, the SS, and COD from producing each ton of paper were 2 kg and 30 kg, respectively. The mill did not test for BOD, however. With regard to the cooperating mill’s raw material supply, Tetrapak bales at 30 maximum were used, in other words, about 6 ton of fibers from Tetrapaks were blended with other raw material sources. Each Tetrapak bale has weight of ca. 220 kg.
In the study, we used effluent obtained from pulping meal boxes stock at 1.0% consistency, 50℃, for 1 h and then disintegrated using a low consistency hydraulic type pulper for 15 min for treatment simulation. The simulating post-consumer meal boxes effluent at before and after pulper were tested. Because used meal boxes have scraped off food residues, but still contain food-derived substances, the SS was much higher than that of unused meal boxes. Also, the groups with better disintegration efficiency contained higher SS. Based on estimations; each ton of waste meal boxes shall generate ca. 10-30 kg of SS, much greater than the mill SS level. The post pulper effluent contained grease absorbed by meal boxes and led to high effluent COD which was derived from grease released after pulp disintegration. At a 2% pulp consistency, COD reached 1373.3 mg/L, indicating a simultaneous increase of COD with pulping efficiency. Since the cooperating mill do not check effluent BOD, while addition of enzyme could affect effluent BOD, hence, we also conducted before and post pulping effluent sample of the pilot-scale study for BOD tests. The results indicated that the trend of BOD change has similar trend as that of COD.
In the pulping experiment, in order to increase fiber recovery of wastepaper meal boxes, the heating temperature and pulping time were the main factors; allowing recovery rate to crease from 29% to ca. 50%. Although modulting pulp pH could increase fiber yield by about 10% (from 50% to 62%), however, the chemicals added (H2SO4, NaOH) have corrosivity, possibly leading to excess amount of fines. Finally, we resolve the problem by using a lower operational temperature in conjunction with enzymes in pulping. The operational conditions were heating temperature, 50℃; heating time 1 h, pulping time 15 min, enzyme B dose at 15% to dry pulp, pulp consistency of 2%. Under such conditions, fiber yield could be increased to 65%, while temperature and pulping time were reduced with significant energy saming. In addition, the conditions posed less damages to fiber and shall help increase unit production pulping efficiency.
As for the pilot-scale experiments, heating at 90℃, 1% pulp consistency, heating time for 1 h could achieve a maximum fiber yield of 66%. If PE film mass was deducted, a fiber recovery rate of 78% was obtained. In actual mill operational estimation, by referencing the operational processes established in this project, we estimate a 30% increase in wastepaper meal boxes pulping efficiency (from 40% to 70%). If by assuming a 220 kg wastepaper bale, and daily usage of 30 bales, this would translate to a daily increase of 1980 kg of fibers. At current short fiber price of NT$15,000/ton, a monthly saving of NT$891,000 could be achieved. Furthermore, by optimizing the cooperating mill’s pulping conditions, we estimate that an overall fiber yield increase of 1% could be achieved, which translate to a monthly saving of NT$750,000.
The proposed future work of this project mainly includes the following:
1) Evaluation of the economic benefit:
Economic benefit estimation: By synthesizing the multifactor costs, operational considerations of the experimental results and scale-up experimental results to estimate the economic benefit of recycling waste paper meal boxes etc.
Incentive calculation: Based on actual operational parameters, proffer a more suitable subsidy standard for such waste paper containers. The subsidy rate can then be basic information for the government’s program in promoting recycling.
Recommendations: In addition to the perspectives of the industry, the team conducting the project has kept the ideal of maintaining environmental health and educating people. We shall use the information obtained in the experimental, and operational process to produce a direction that people can accept and adopt which can be a basis of governmental promotion of waste paper container recycling program.
2) Integration of marketing channels: in order to achieve the goal of increasing the current 40.9 ton/annuam waste paper container recycling rate to 500 ton/annum, in addition to cooperating in full mill experiment, mill operational condition modification, more importantly negotiation and integration of the resources of various marketing channel merchants to produce a heightened possibility of achieving the goal.
Integration of the information on market channel merchants: Market channel merchants have broad contents, including the upstream waste paper container recycling merchants, and the downstream handling facility operators that might take over the treatment of substances generated by the recycling process. However, these channels have differing natures and the managers often have different precept as well.
Coordinating the market channel merchants: Because items provided by the waste paper container recycling merchants are diverse, after coordinating and integrating the information, the project provides a means to understand the willingness of the individual merchant to accept guidance, and explaning to them the optimal final flow of the recovered waste paepr containers.
|