Earticle

전국 공공하수처리장의 80% 이상이 우기시 처리장에 유입수가 2Q~3Q까지 유입되고 있어 하수월류수에 의한 하수처리공정관리에 많은 난제를 안고 있는 실정이다. 본 기술은 하수월류수를 급속처리하는 장치로써 최단시간(15분)에 하수월류수를 깨끗이 처리하는 하수월류수 다이렉트 급속처리 기술이다. 핵심기술은 3가지로 인라인 고속응집 및 무동력 플럭응결장치, Splitter Type 고효율 마이크로버블장치, 국내최초로 개발한 다단격벽식 고효율 부상분리 장치로 이루어져 있다. 원리는 1단계 응집·응결, 2단계 마이크로버블을 이용한 버블코팅, 3단계 3단 부상조를 이용한 버블코팅된 응집입자들의 부상으로 이루어진 굉장히 심플한 공정이다. 강우시 실험결과, GJ-R 공법을 통과한 하수월류수가 SS 98.6%, BOD 88.8%, COD 85.1%, TN 21.7%, TP 92.1%의 높은 제거효율을 보이는 것을 볼 수 있었으며, 처리수의 SS 2.8 mg/L, BOD 11.2 mg/L, TP 0.24 mg/L로 환경부 간이공공하수처리시설 수질기준인 BOD 60 mg/L 이하로써 공법의 응집·응결 및 마이크로버블 부상 효율이 굉장히 우수한 것을 볼 수 있었다.

More than 80% of the public sewage treatment plants in the country are receiving influent water (2Q~3Q) during rainfall. This technology is a sewer overflows direct treatment technology that cleans sewer overflows in the shortest time (15 minutes). The core technology is quite simply composed of three device (high-speed flocculation and non-motorized flux condensing device, splitter type high efficiency microbubble system, multi-stage type bulkhead flocculation tank). The experimental results during rainfall, the final effluent removal efficiency of SS (98.6%), BOD (88.8%), COD (85.1%), TN (21.7%), TP 92.1%) were much higher than existing treatment facilities. and When viewing the water quality of effluent of SS 2.8 mg/L, BOD 11.2 mg/L (Convenience public sewage treatment plant water quality standards of BOD 60 mg/L), TP 0.24 mg/L, The present process can be seen that a very good efficiency of coagulation·flocculation, microbubble floatation.

본 연구의 목적은 호주산 저품위 동광을 부유선별하여 정광으로 회수하고자 할 때, 최적의 부유선별 조건을 얻고자 하는데 있다. 본 연구에서는 저품위 동광의 파분쇄 및 분급에 의해 선별에 적절한 입자크기의 시료를 얻은 다음, 이를 대상으로 부유선별 시 포수제, 활성제, 억제제의 첨가량 및 광액의 pH 변화가 부선효율에 미치는 영향을 조사함으로써 품위가 향상된 정광을 얻고자 하였다. 본 연구실험결과 얻은 최적의 부유선별 조건은 광액산도 pH9.0, 활성제 500 g/t CuSO4·5H2O, 포수제 500 g/t K.E.X, 억제제1500 g/t Na2SO3, 광액농도는 25 wt.% 이었다. 최적조건하에서 얻은 정광중의 동 품위 및 회수율은 각각 4 wt.%와 65 wt.% 정도이었고 대부분 철 성분을 함유한 광물 이었다.

The purpose of this study is to obtain an optimum condition of the concentrate by floatation using Australian low grade copper ore of suitable particle size by crushing, grinding and sizing. The effect of the dosage of collector, activator, depressant and change of acidity on the floatation was investigated. The floatation conditions comprising of pH 9.0 acidity, 500g/t CuSO4·5H2O activator, 500g/t K.E.X. collector, 1500g/t Na2SO3 depressant and 25wt.% plup density were optimized. Grade and recovery of copper in the concentrate obtained by froth floatation under optimum conditions were 4wt.% and 65wt.% respectively.

본 연구는 대주주, 증권사 및 투자자간 정보 보유 정도가 각각 상이한 유상증자라는 경제적 사건을 중심으로 발행사 대주주의 보유지분율에 따른 경제적 유인이 유상증자의 방식 및 증권사와의 주간사 계약에 어떠한 영향을 미치며, 궁극적으로는 이들이 발행 가격 결정에 어떠한 영향을 미치는지 분석한다. 실증분석 결과 첫째, 대주주 지분율이 높을수록 발행사는 주주우선배정 방식보다는 주주배정 방식을 선호하고, 반대의 경우 주주우선배정 방식보다는 일반공모 방식을 선호하였다. 이는 대주주가 발행사에 대한 우월한 정보 보유를 바탕으로 발행사에 대한 관여를 통하여 이윤을 추구하며, 일반 투자자로의 부의 이전을 피하고자 하는 경제적 유인에 기인하는 것으로 해석된다. 둘째, 주주우선배정 방식하에서 발행사는 총액/잔액인수 계약을 체결하는 것으로 나타났다. 이는 실권주 인수 미달발생 위험에 따른 대주주의 잠재적인 경제적 손실을 최소화하기 위한 것으로 해석된다. 이때 상대적으로 명성이 낮은 증권사일수록 거래의 수임을 위하여 총액/잔액인수 계약을 체결하는데 적극적인 것으로 나타났다. 셋째, 주주우선 배정 방식 및 총액/잔액인수 계약의 경우, 상대적으로 저평가 정도가 높은 것으로 나타났다. 이는 유상증자의 확실한 성공을 원하는 대주주와 중개위험을 기피하고자 하는 증권사간 이해상충문제가 타협된 결과로 해석된다.

This study analyses how the economic interests of a company’s largest shareholders affect the choice of secondary equity offering (“SEO”) floatation methods, forms of underwriting agreements with investment banks, and ultimately, the new share issuance price in a SEO where the information asymmetry is high amongst the largest shareholders, investment banks and investors. Unlike price discovery through bookbuilding process, issuing companies and investment banks determine issuance price prior to the offering in Korea. The SEO floatation methods and forms of underwriting agreement are publicly disclosed. This study differs itself from previous studies in that it evaluates how the economic interests of the largest shareholders as well as potential conflicts of interests amongst SEO participants may impact the selection of SEO floatation methods and forms of underwriting agreement. Furthermore, this study, by presenting the drivers behind a SEO and by analysing its effects, is anticipated to contribute to future research related to securities issuance, which is one of the most important financial decisions for corporations. The largest shareholders are seeking not only economic profits from SEO but also noneconomic objectives such as strengthened management control of the corporation. Investment banks tend to prioritize the relationship with the largest shareholders of the issuing company over the interests of retail investors. The forms of SEO can be classified into rights offering, rights offering with under subscribed shares to be offered to the public(“ROUP”), public offering, and 3rd party allotment. There are two types of underwriting agreements which include underwriting agreements on a firm commitment basis and best efforts basis. This study excludes cases where SEO is based on 3rd party allotment as well as those cases where underwriting agreements are non-existing. This study examines which floatation method of SEO is preferred according to the stakes of the largest shareholders and also identifies the financial variables which may have impact on the floatation method of SEO and forms of underwriting agreement chosen. Firstly, based on the analysis of precedent SEOs, we found that the higher the stake of the largest shareholders or the healthier the profitability and financial structure of a company, rights offerings is most preferred and public offering is least preferred. ROUP comes in between the rights offerings and public offerings. The main reason behind such outcome comes from the economic incentives of the largest shareholders. The largest shareholders take advantage of the situation where they possess superior information on the company relative to the retail investors. When the largest shareholders have higher stakes and therefore more economic interests, they tend to get more involved in the SEO process which could affect the economic benefit of minority investors and try to maintain or increase their existing stakes or trade preemptive rights to pursue economic interests. When the largest shareholders have lower stakes and therefore less economic rights, as long as the management control is secured, they tend not to commit more capital to maintaining their stakes not to share potential economic gains with outside investors because they’ve already disposed of significant stakes. Instead they’d rather seek another investment opportunity. In addition, outside investors would consider the largest shareholders’ trading of preemptive rights negative so that public offering is likely a choice of SEO floatation method in this case. Secondly, under ROUP, issuers prefer underwriting agreements on a firm commitment basis to minimize largest shareholders’ potential economic losses associated with under subscribed shares. The largest shareholders influence issuers to negotiate with investment banks to reflect their interests in the underwriting agreement. The less reputable investment banks aggressively take the risk of entering into an underwriting agreement on a firm commitment basis to get mandated for the SEO. The largest shareholders prefer underwriting agreement which guarantees that new shares be fully subscribed not to suffer from losses associated with under subscription which in turn has a negative effect on stock prices. On the other hand, in the case of public offerings where retail investors participate, the economic interests of the largest shareholders are less of importance and thus, issuers are indifferent to either form of underwriting agreement. Thirdly, under ROUP and underwriting agreements on a firm commitment basis, the level of discount and underpricing of issuance price is higher than that of the other SEO methods. This is the outcome of compromise of the conflicts of interests between the largest shareholders who want guarantee of the success of SEO and investment banks which want to minimize their underwriting risks. On the other hand, under underwriting agreements on a best efforts basis, because investment banks do not bear underwriting risks and only focus on the sale of new shares, they are not sensitive to the issuance price so there is no incentive for them to reduce the level of discount and the issuance price.

The harvesting of microalgae is a critical step that precedes biodiesel conversion. The most widely used harvesting technology is flocculation and floatation. In this study, the efficiency of the flocculants aluminum sulfate and poly aluminum chloride were evaluated for harvesting the alga Dunaliella tertiolecta in conjunction with dissolved air floatation. Using the jar test the optimum concentration range for aluminum sulfate was 1.0~1.5 g/L and for poly aluminium chloride, 1.5~2.0 g/L. The degree of coagulation was visualized by microscopy. Further analysis in combination with dissolved air floatation showed that the optimal concentration for aluminum sulfate was 1.1 g/L and for poly aluminum chloride, 1.6 g/L.

Cryptosporidium can cause gastrointestinal diseases worldwide, consequently posing public health problems and economic burden. Effective techniques for detecting contaminated oocysts in water are important to prevent and control the contamination. Immunomagnetic separation (IMS) method has been widely employed recently due to its efficiency, but, it is costly. Sucrose floatation technique is generally used for separating organisms by using their different specific gravity. It is effective and cheap but time consuming as well as requiring highly skilled personnel. Water turbidity and parasite load in water sample are additional factors affecting to the recovery rate of those 2 methods. We compared the efficiency of IMS and sucrose floatation methods to recover the spiked Cryptosporidium oocysts in various turbidity water samples. Cryptosporidium oocysts concentration at 1, $10^1$, $10^2$, and $10^3$ per $10{\mu}l$ were spiked into 3 sets of 10 ml-water turbidity (5, 50, and 500 NTU). The recovery rate of the 2 methods was not different. Oocyst load at the concentration < $10^2$ per 10 ml yielded unreliable results. Water turbidity at 500 NTU decreased the recovery rate of both techniques. The combination of sucrose floatation and immunofluorescense assay techniques (SF-FA) showed higher recovery rate than IMS and immunofluorescense assay (IMS-FA). We used this SF-FA to detect Cryptosporidium and Giardia from the river water samples and found 9 and 19 out of 30 (30% and 63.3%) positive, respectively. Our results favored sucrose floatation technique enhanced with immunofluorescense assay for detecting contaminated protozoa in water samples in general laboratories and in the real practical setting.

Cyst nematodes, some of the most important plant-parasitic nematodes globally, cause major damage to Chinese cabbage and soybean plants in Korea. Cysts are commonly used for cyst nematode bioassays because many eggs are included inside cyst. Traditionally, cysts are extracted from the soil using the paper strip method or the centrifugal flotation method (CFM) combined with sieving. The specific gravity of sugar solution (SGSS) is often used in the CFM; however, the efficiency of cyst extraction and egg hatching in the CFM has not been studied. In this study, we assessed the effects of SGSS in a specific gravity range of 1.15 to 1.30 in the CFM on the cyst extraction and egg hatching of clover cyst nematode (Heterodera trifolii) and sugar beet cyst nematode (H. schachtii). High SGSS in the CFM within the range of 1.15 to 1.30 was positively correlated with the extraction of more cysts. Egg-hatching rates were not different between SGSSs, indicating that SGSS did not directly affect egg-hatching rates. These results showed that the cysts of cyst nematodes can be efficiently extracted with high SGSS in the CFM.

In an effort to compare parasite egg detection efficiencies, fecal samples from 231 dairy and Korean native cattle in the area of Hongsung - Gun, Kangwon-Do, were examined by the sedimentation and floatation methods. The results obtained were summarized as follows : 1. Detection rates of Fasciola hepatica were 27.2% by the sedimentation method and 61.6% by the floatation method, and those of Paramphistomum spp., were 48.9% and 66.2% respectively. 2. In the Fasciola hepatica, the numbers of cattle contained over a hundred eggs were one by the sedimentation method, but ten by the floatation method. For the Paramphistomum spp., the numbers of cattle contained over a hundred eggs were six by the sedimentation method, but thirty three by the floatation method. Thus, the number of the parasite eggs detected were greater when examined by the floatation method than by the sedimentation method. 3. The numbers of cattle from which eggs were detected only by the sedimentation methods were three and four for Fasciola hepatica and Paramphistomum spp., respectively, while those by the floatation method only were 55 and 44. respectively. 4. Trematodes, nematodes. protozoa and cestodes were floatated by the floatation method using zinc sulfate solution (specific gravity 1.27).

미세플라스틱이 물 환경으로 배출되는 주요 경로로는 하수처리장 방류수와 강우유출수가 있다. 하수처리장 및 유역에서 배출된 미세플라스틱은 하천과 하구역을 거쳐 해양과 같은 대규모 수역으로 이동하는데, 이 과정에서 해양뿐만 아니라 담수호, 저수지 등과 같은 공공수역에도 미세플라스틱이 지속적으로 축적되고 있다. 특히 강우유출수에 포함된 미세플라스틱은 적절한 처리 과정 없이 하천으로 유입되는 경우가 많아 공공수역 내 미세플라스틱 저감 기술의 필요성이 증가하고 있다. 그러나 미세플라스틱 관련 기존 연구는 미세플라스틱의 분포 등 현황에 대한 모니터링 및 환경위해성과 관련한 것이 대부분이며, 미세플라스틱 저감기술 관련 연구 또한 일부 정수처리 및 하수처리 공정을 대상으로 하는 초기 단계의 연구가 진행되고 있을 뿐 공공수역에서의 미세플라스틱 저감기술 개발 관련 연구는 전무한 실정이다. 따라서, 본 연구에서는 기존의 물리·화학적 수처리 공정인 용존공기부상법(Dissolved Air Flotation, DAF)에 물의 전기분해 시발생하는 브라운가스를 활용하여 응집된 물질을 빠르게 부상시켜 수체 내 오염물질을 제거할 수 있는 기술을 통해 수체 내 미세플라스틱 저감효과를 분석하였다. 또한, 해당 기술을 공공수역인 저수지에 적용하여 오염물질과 함께 미세플라스틱을 제거할 수 있는지 검토하였다.

국내 Y정수처리시설에 20-40 m³/m²/h의 표면부하율을 갖는 고속 용존공기부상공정을 도입하였다. 우선, 용존공기부상공정과 입상활성탄 공정이 결합된 반응기를 일처리용량 500 m³/day의 조건으로 운전하였다. 운전결과는 두 공정이 원수내 탁도, 조류, 지오스민, 2-MIB를 감소시킬 수 있음을 증명하였다. 도출된 최적 설계요소를 활용하여 현장규모의 공정(5,000 m³/day)에 용존공기부상공정을 도입하였다. 여름철 56일간 조류와 탁도 제거율을 평가하였다. 처리수 내 조류의 개체수는 20-30 cells/mL 이하로 유지되었으며, 조류 제거효율은 80-89%를 기록하였다. 침전법 및 용존공기부상공정 처리수질의 탁도 제거효율을 비교한 결과 평균 탁도 제거효율은 77%를 나타냈다. 이러한 결과들은 고속 용존공기부상공정이 여름철 음용수의 탁도 및 조류와 같은 저밀도 고형물을 제거하는데 유의미한 방법임을 나타냈으며, GAC는 맛·냄새를 유발하는 화합물(지오스민, 2-MIB)를 제거할 수 있는 공정 옵션인 것을 확인하였다.

A high-rate dissolved air flotation (DAF) process, with a surface loading rate of 20-40 m³/m²/h, was introduced at the Y-Drinking Water Treatment Plant in South Korea. First, the DAF and granular activated carbon (GAC) processes were combined in the reactor, and the pilot plant was operated at 500 m³/day. The results from these tests demonstrated that there were significant decreases in turbidity, algae, geosmin, and 2-methylisoborneol (2-MIB) following implementation of the two processes. Then, the optimum design factors were used and the DAF system was introduced at the field-scaled plant (5,000 m³/day). The removal rate of algae and turbidity was evaluated over 56 days in summer. The number of algae in the treated water was maintained at below 20-30 cells/mL, which represented an algae removal efficiency of 80-89%. The effluent turbidity was compared to the conventional sedimentation and DAF processes, and the average turbidity removal efficiency was 77%. These findings indicate that the high-rate DAF process is a promising method for the removal of low-density solids such as turbidity and algae during the treatment of drinking water, especially in summer. Additionally, GAC represents an acceptable treatment option to remove taste-and-odor-causing compounds (e.g., geosmin and 2-MIB).

수산 시설물의 내구성을 평가하기 위한 기초 단계로 부력재 또는 프레임용 재질로 많이 사용되고 있는 국산 고밀도 PE 및 고강도 PVC와 노루웨이 고밀도 PE에 대하여 인공 광원을 조사한 후 시간의 경과에 따른 시료의 물성과 그 표면 및 파면의 형태적 변화를 비교$\cdot$분석하였다. 실험에서 얻어진 결과를 요약하면 다음과 같다. 1) 자외선 조사 시간이 경과됨에 따라 세 시료 모두 인장 응력과 탄성률은 미처리된 초기의 그것보다 크게 감소하였으나, 파단 신장률의 경우 처음에는 증가하다가 다시 감소하는 불규칙적인 경향을 나타내었다. 2) 잔여 응력 RS(kg/mm 상(2))와 자외선 폭로 기간 Y(Year)와의 상관 관계는 다음과 같이 나타났다. KHDPE : RS=2.6769-0.0003Y(r 상(2)=0.63) Hi-PVC : RS=5.3470-0.0003Y(r 상(2)=0.91) NHDPE : RS=2.4929-0.0004Y(r 상(2)=0.97) 3) 전자 현미경 촬영 결과, 자외선의 영향으로 시료의 표면에 물방울 형상이 나타났으며, 자외선 조사 시간이 경과됨에 따라 분자 구조의 분해로 인하여 작은 구멍이 확인되었다.

In order to analyze the photodegradation of plastic materials for floats or frames of fisheries facilities, weathering experiment on 3 kinds of plastic materials like high density PE of Korea(KHDPE) and Norway(NHDPE) and high strength PVC(Hi-PVC) was carried out during 900 hours exposure by using xenon light source of weather-Ometer. The results obtained are as follows; With increasing of ultraviolet radiation(UVR) time, a remarkable losses in the mechanical properties of each specimen were observed except for the remaining strain of HDPE materials. As NHDPE lost almost 15% of its initial tensile stress during a 900 hours exposure followed by KHDPE 12% and Hi-PVC 6%. In addition, the remaining tensile stress RS(kg/$mm^2$) decreases almost linearly with the lapse of exposure time to light Y(Year) and the empirical equations of each specimen computed as follows; KHDPE : RS=2.6769-0.0003Y($r^2$=0.63) Hi-PVC : RS=5.3470-0.0003Y($r^2$=0.91) NHDPE : RS=2.4929-0.0004Y($r^2$=0.97) It was observed by scanning electron microscope that all specimens with UVR time had started to decompose and had bubbled areas and small holes.