Sludge Thickener Research Articles

STUDY OF COMMUNAL BASIUNI IMRAN ISLAMIC BOARDING SCHOOL WASTEWATER TREATMENT PLANT (WWTP) IN SAMBAS REGENCY

Islamic Boarding School has a treatment capacity of 33 m3 and an area of 24 m2. Based on the results of initial wastewater quality tests on communal WWTP, the TSS, COD, and BOD parameters are above the quality standard threshold based on the Wastewater Quality Standard of the Minister of Environment Regulation Number 68 of 2016. This evaluation aims to determine the processing efficiency of communal WWTP and evaluate the processing unit in communal WWTP as well as alternative improvements that effectively reduce the parameters of pH, TSS, BOD, COD, and fatty oils. This research method is descriptive analytics, which analyses problems from data collected descriptively to find solutions to problems. The results of this evaluation show that the TSS, COD, and BOD parameters are above the quality standard threshold. The pH parameter increased by 3.6%, removal efficiency for BOD by 76.4%, COD by 71.9%, TSS by 84.3%, and oil grease by 91.9%. Alternative WWTP improvements are carried out by redesigning the Communal WWTP, which consists of calculating the equalization unit, precipitator I, anaerobic filter, Precipitator II, disinfection, and sludge thickener, Sludge digester, sludge drying bed and analysis of the Budget Plan Cost (RAB). The communal WWTP redesign requires a land area of 52.62 m2 with a processing capacity of 56.8 m3 and a cost budget plan of Rp.157,224,000.00. The redesign results of this evaluation can reduce environmental impacts due to domestic wastewater.

Wastewater treatment plant design and modeling for the city of Erzurum

Currently large amounts of wastewater are produced by domestic and industrial activities. Discharge of wastewater to the receiving environment without treatment causes significant health and environmental problems. Modeling and optimization of Wastewater Treatment Plants (WWTP) developed to treat domestic wastewater play key roles in determining unit components, design parameters and operation conditions. Several models were proposed to predict the treatment performance in WWTP. The Activated Sludge Model No. 1 (ASM1) is one of the commonly-used standard models developed to better understand removal of carbonaceous and nitrogenous materials. In this study, a WWTP is proposed for domestic wastewater using grit chamber, circular primary and secondary clarifiers, completely-mixed aeration tank, sludge thickener, sludge dewatering and anaerobic digestion processes together. The WWTP was modeled with ASM1 noting the topographic and meteorological features of the city. The treatment performances with wastewater temperatures of 10°C and 20°C were investigated for this plant, operating at high elevation. Removal efficiencies at 20°C were 95.7%, 92.2%, 97.9% and 99.2% for MLSS, COD, BOD and NH4, while effluent concentrations were 14.83, 48.51, 6.55 and 0.3 mg L-1, respectively. At 10°C, removal efficiencies were 88.9%, 88%, 93.2%, and 26.9%, while effluent concentrations were 38, 75, 21.83 and 26.13 mg L-1, respectively. A clear reduction was observed in nitrogenous material removal at low temperatures. Additionally, keeping dissolved oxygen concentration in the aeration tank at 1.5 mg L-1 with PID control increased nitrification efficiency by 30%. The findings reveal the importance of modeling studies during planning of WWTP.

Production of Drinking Water with Membranes with Simultaneous Utilization of Concentrate and Reject Effluent after Sludge Dewatering.

A new technology is described that enables us to completely exclude liquid discharges during production of drinking water from surface sources. The proposed described technological scheme separates the natural water into a stream of purified drinking water and dewatered sludge. The sludge moisture has a value of 80 percent. The experimental program is described to treat the natural water with nanofiltration membranes and to produce a drinking-quality water with recovery value of 0.99 and higher. Concentrate of membrane plant is mixed with the wet sludge and the reject effluent after sludge dewatering is again treated by reverse osmosis membranes and returned back to the sludge thickening tank. Results of experiments to treat reject water after sludge dewatering are presented. The use of nanofiltration membranes provides reduction in the Total Dissolved Solids content (TDS), aluminum, color and oxidation to meet drinking water standards. Experimental plots are presented that can be used to select membrane characteristics and to predict product water chemical composition at each stage of the membrane treatment scheme. Concentrate of membrane treatment plant is mixed with the wet sludge in the thickening tank. The sludge, after the thickening tank, is dewatered using either filter-press or centrifugal equipment. The reject (or fugate), after sludge dewatering, is treated by membrane facility to separate it into deionized water stream and concentrate stream. The deionized water can be mixed with the feed water or drinking water and the concentrate stream is returned back to the thickening tank. Thus, the salt balance is maintained in the thickening tank, whereby all dissolved salts and impurities that are rejected by membranes are collected in the thickening tank, and then are withdrawn together with the dewatered sludge. Based on the results of experimental data processing, balance diagrams of the sludge dehydration process with waste water purification at the membrane plant and with the addition of the membrane plant concentrate to the sludge thickener are presented, according to which all contaminants removed by the membranes are removed together with the sludge.

Effects of different nitrogen/phosphorus ratios on the growth and metabolism of microalgae Scenedesmus obliquus cultured in the mixed wastewater from primary settling tank and sludge thickener

Microalgae has great potential in wastewater treatment and resource utilization, but few studies have explored the impact mechanism of pollutants on its biochemical compositions. In this study, the effects of different ratios of nitrogen to phosphorus (N/P) on microalgae Scenedesmus obliquus grown in the mixed wastewater from primary settling tank (PSW) and sludge thickener (STW) were investigated. The optimum N/P ratio for the growth of S. obliquus was determined by nutrient utilization rates and the growth curve. On this basis, the effects of different N/P ratios on its biochemical compositions were explored, and reasons were further analyzed by proteomics. Results showed that at N/P=18, the growth of S. obliquus was optimal (OD680=2.34). And dry weight, lipid production, and chlorophyll-a accumulation were highest (1.70 g·L-1, 0.49 g·L-1, 7.43 mg·L-1), whereas protein production was lowest (0.10 g·L-1). Proteomic results showed that the metabolic activities of S. obliquus cells were the most active at N/P=18. Productivity processes were involved in protein up-regulation, producing more energy. Furthermore, lipid metabolism and fatty acid synthesis pathways were strengthened. The ribosome synthesis activity was significantly enhanced, but the protein content was low, which might attribute to the energy generated by the production activity for other activities.

Emergence of blaNDM-1, blaNDM-5, blaKPC-2 and blaIMP-4 carrying plasmids in Raoultella spp. in the environment

To date, carbapenem-resistant Enterobacteriaceae have been found predominantly in clinical settings worldwide. Raoultella belongs to the Enterobacteriaceae family which can cause hospital-acquired infections, and carbapenem-resistant Raoultella spp. (CRR) is sporadically reported in the environment. We investigated the distribution and underlying resistance mechanisms of CRR in a wastewater treatment plant (WWTP) from eastern China between January 2018 and February 2019. A total of 17 CRR were isolated from 324 environmental samples, including Raoultella ornithinolytica (n = 15) and Raoultella planticola (n = 2). The detection of CRR was more frequent in the water inlet compared to anaerobic tank, aerobic tank, sludge thickener, activated sludge, mud cake storage area, and water outlet, and CRR was detected in mud cake stacking area. All CRR were resistant to imipenem, meropenem, ampicillin, piperacillin-tazobactam, cefotaxime, ceftazidime, trimethoprim-sulfamethoxazole and fosfomycin. Four different carbapenemase genes were identified, including blaKPC-2 (n = 13), blaNDM-1 (n = 8), blaNDM-5 (n = 1), blaIMP-4 (n = 1). Interestingly, isolated R. ornithinolytica from the WWTP were closely related to those reported from human samples in China. Plasmid analysis indicated that IncFII(Yp), IncP6, and IncU mediated blaKPC-2 spread, IncX3 and IncN2 mediated blaNDM spread in the environment. The core structure of the Tn3-ISKpn27-blaKPC-2-ISKpn6, ISAba125-blaNDM-bleMBL-trpF-dsbD were identified. The study provides evidence that Raoultella spp. may spread alarming carbapenem resistance in the environment and, therefore, the continuous surveillance for carbapenem resistance in the WWTP should be conducted, especially sludge.

Transport and accumulation of microplastics through wastewater treatment sludge processes

Wastewater treatment plants (WWTPs) are important routes for releasing microplastics into the environment, with the produced sludge acting as a recipient of microplastics from wastewater. There is little information on the impact of sludge processes on the number of microplastics in sludge. In this study, the presence of microplastics in sludge produced by the Sari WWTP in northern Iran was investigated. Samples were taken in 3 replications and microplastics larger than 37 μm were extracted. The sludge from primary settling tank, clarifier, after sludge thickener and after aerobic digester, and after dewatering contained 214, 206, 200, 238, and 129 microplastics/g dry weight, respectively. According to the amount of sludge produced for each unit, this equals 280, 362, 599, 601, and 276 million microplastics/day, respectively, of which more than 85% were fibers. The numbers of microplastics in the sludge from the output of the sludge thickener and the aerobic digester did not significantly differ. However, their numbers decreased by more than 50% after dewatering, probably due to the destruction of flocs in the digestive process and the release of attached microplastics, which are returned into the wastewater treatment process with the rejected water. Polyester and polyethylene were the predominant types of fibers and particles, respectively. Given the annual amount of sludge produced, more than 100 billion microplastics enter the environment per year. Wastewater sludge, therefore, is an important source for the emission of microplastics, especially fibers, to the environment, warranting further evaluation of the associated environmental hazards.

The fate of SARS-COV-2 in WWTPS points out the sludge line as a suitable spot for detection of COVID-19

SARS-CoV-2 genetic material is detectable in the faeces of a considerable part of COVID-19 cases and hence, in municipal wastewater. This fact was confirmed early during the spread of the COVID-19 pandemic and prompted several studies that proposed monitoring its incidence by wastewater. This paper studies the fate of SARS-CoV-2 genetic material in wastewater treatment plants using RT-qPCR with a two-fold goal: i) to check its presence in the water effluent and in the produced sludge and ii) based on the understanding of the virus particles fate, to identify the most suitable spots for detecting the incidence of COVID-19 and monitor its evolution. On the grounds of the affinity of enveloped virus towards biosolids, we hypothesized that the sludge line acts as a concentrator of SARS-CoV-2 genetic material. Sampling several spots in primary, secondary and sludge treatment at the Ourense (Spain) WWTP in 5 different days showed that, in effect, most of SARS-CoV-2 particles cannot be detected in the water effluent as they are retained by the sludge line. We identified the sludge thickener as a suitable spot for detecting SARS-CoV-2 particles thanks to its higher solids concentration (more virus particles) and longer residence time (less sensitive to dilution caused by precipitation). These findings could be useful to develop a suitable strategy for early warning of COVID-19 incidence based on WWTP monitoring.

Feasibility analysis for reduction of carbon footprint in a wastewater treatment plant

This study presents an integrated feasibility analysis approach to reduce the carbon footprint in the largest Italian wastewater treatment plant (WWTP). Firstly, a model-based feasibility analysis was carried out to assess the applicability of upgrading scenarios, for an ongoing anaerobic sludge digestion process. Application of dynamic sludge thickener, as well as hybrid thermo-alkali pre-treatment of waste activated sludge, were assessed to enhance the biogas production in the WWTP. Further, an implementation of the selective membranes was proposed and studied to upgrade the produced biogas in sludge treatment units to biomethane with an average efficiency of 98.6%. Model-based sludge pre-treatment and biogas upgrading strategies were developed and evaluated in terms of mass, energy, and greenhouse gas emission balance. The obtained results prove that practicing the proposed upgrading scenario can lead to an 18% improvement in biogas production and a significant reduction of thermal energy auto-consumption and total greenhouse gas emissions. In the second phase, the laboratory-based feasibility analysis was performed about the integration of microalgae technology into the current process of the WWTP. A planar photobioreactor was built to estimate the volumetric mass transfer coefficient (KLa) and CO2 consumption of the reactor. By the use of 44 and 76 μmol/m2/s light intensities, the results show 80% and 70% reductions in total CO2, respectively. The tested configuration guaranteed 11.763 and 27.943 mg/l/h CO2 consumptions, as well as 0.5775 h−1 and 17.7 h−1 KLa values. Overall, the results prove that applications of the technologies proposed in this study can significantly reduce the carbon footprint of the WWTP.

Drive Unit for Sludge Collectors, Thickeners and Clarifiers

Drive Unit for Sludge Collectors, Thickeners and Clarifiers

Effects of in-sewer dosing of iron-rich drinking water sludge on wastewater collection and treatment systems

The use of coagulants and flocculants in the water and wastewater industry is predicted to increase further in the coming years. Alum is the most widely used coagulant, however, the use of ferric chloride (FeCl3) is gaining popularity. Drinking water production that uses FeCl3 as coagulant produces waste sludge rich in iron. We hypothesised that the iron-rich drinking water sludge (DWS) can potentially be used in the urban wastewater system to reduce dissolved sulfide in sewer systems, aid phosphate removal in wastewater treatment and reduce hydrogen sulfide in the anaerobic digester biogas. This hypothesis was investigated using two laboratory-scale urban wastewater systems, one as an experimental system and the other as a control, each comprising sewer reactors, a sequencing batch reactor (SBR) for wastewater treatment, sludge thickeners and anaerobic digestion reactors. Both were fed with domestic wastewater. The experimental system received in-sewer DWS-dosing at 10 mgFe L−1 while the control had none. The sulfide concentration in the experimental sewer effluent decreased by 3.5 ± 0.2 mgS L−1 as compared with the control, while the phosphate concentration decreased by 3.6 ± 0.3 mgP L−1 after biological wastewater treatment in the experimental SBR. The dissolved sulfide concentration in the experimental anaerobic digester also decreased by 15.9 ± 0.9 mgS L−1 following the DWS-dosing to the sewer reactors. The DWS-doing also enhanced the settleability of the mixed liquor suspended sludge (MLSS) (SVI decreased from 193.2 ± 22.2 to 108.0 ± 7.7 ml g−1), and the dewaterability of the anaerobically digested sludge (the cake solids concentration increased from 15.7 ± 0.3% to 19.1 ± 1.8%). The introduction of DWS into the experimental system significantly increased the COD and TSS concentrations in the wastewater, and consequently the MLSS concentration in the SBR, however, this did not affect normal operation. The results demonstrated that iron-rich waste sludge from drinking water production can be used in the urban wastewater system achieving multiple benefits. Therefore, an integrated approach to urban water and wastewater management should be considered to maximise the benefits of iron use in the system.

Study on the application of nitritation, treating different wastewater streams with high nitrogen content

As water pollution associated with nitrogen and its compounds become more epidemic, the seriousness of water pollution resulting from excessive amount of nitrogen becomes magnified. A number of studies were conducted to reduce nitrogen content in a variety of wastewater streams. In particular, the study of nitritation as an innovative method of nitrogen removal method had a relatively high attention because of its cost-effective benefit and environmentally benign process as proven. However, the research and development on the applicability and the operating efficiency of the nitritation has not been well known. In addition, nitritation was not applied to feasibly treat different wastewaters with variable contents of nitrogen. Accordingly, the current study was designed to analyze the characteristics of various wastewaters such as domestic sewage, primary clarifier supernatant, sludge thickener supernatant, anaerobic digester supernatant, sludge decanted water, and livestock wastewater. The results exhibited that, by strength, domestic sewage and primary clarifier supernatant were categorized as relatively low concentration wastewater, sludge decanted water as medium strength, and sludge thickener supernatant, anaerobic digester supernatant, and livestock wastewater as relatively high concentration wastewater, which showed very high nitrogen content. Therefore, such high nitrogen content will negatively impact on existing wastewater treatment process and its operating procedure. It was found that nitritation well proceeded with the high removal of ammonium nitrogen and best suitable to treat anaerobic digester supernatant with the highest concentration of ammonium nitrogen.

A comprehensive laboratory assessment of the effects of sewer-dosed iron salts on wastewater treatment processes

The effect of iron-dosing in the sewer system, on wastewater treatment processes, was investigated using laboratory-scale wastewater systems comprising sewers, wastewater treatment reactors, sludge thickeners, and anaerobic sludge digesters. Two systems, fed with real domestic wastewater, were operated for over a year. The experimental system received ferric chloride (FeCl3) dosing at 10 mgFe L−1 in the sewer reactor whereas the control system received none. Wastewater, sludge and biogas were extensively sampled, and analysed for relevant parameters. The FeCl3-dosed experimental system displayed a decreased sulfide concentration (by 4.3 ± 0.5 mgS L−1) in sewer effluent, decreased phosphate concentration (by 4.7 ± 0.5 mgP L−1) in biological treatment reactor effluent, and decreased hydrogen sulfide concentration in biogas (911.5 ± 189.9 ppm to 130.0 ± 5.9 ppm), as compared with the control system. The biological nitrogen removal performance of the treatment reactor, and biogas production in the anaerobic digester were not affected by FeCl3-dosing. Furthermore, the dewaterability of the anaerobically digested sludge was enhanced by 17.7 ± 1.0%. These findings demonstrate that iron-dosing to sewers can achieve multiple benefits including sulfide removal in sewers, phosphorus removal during wastewater treatment, and hydrogen sulfide (H2S) removal during biogas generation. Therefore, an integrated approach should be taken when considering iron salts usage in an urban wastewater system.

Control of hydrogen sulphide in full-scale anaerobic digesters using iron (III) chloride: performance, origin and effects

The study presents the results of sulphide control using iron (III) chloride in full-scale anaerobic digesters (ADs) at a large-scale municipal wastewater treatment plant (WWTP). Iron (III) (‘ferric’) chloride was applied at a range of 24–105 mg FeCl3/L with and without alkali solution using different strategies. Introduction points were implemented at the feeding line and the sludge thickener unit. Response of the ADs in terms of biogas H2S reduction over time, solid loading rates (SLR), feed sludge flow rate and pH level were investigated. Reduction of H2S in the biogas reached 4 035 μg/L in directly-dosed AD versus a 1 345 μg/L drop in non-dosed ADs, as a result of internal recirculation among the digesters, where actual values were possibly higher as volatile solid (VS) degradation increased in all ADs during the dosing period. No noticeable effect on biogas production and pH was observed. The degree of H2S production was found to be correlated to the volatile SLR, where primary sludge solids contributed mostly to the organic and proteinaceous content of the thickened sludge and presented a high variation and a strong relationship with H2S production. Correlation analysis based on data for the 17-month period that followed supported the significant role of primary SLR in H2S production.

BIO-METHANE POTENTIAL TEST FOR ANAEROBIC CO-DIGESTION OF FAECAL SLUDGE AND SEWAGE SLUDGE

Faecal sludge (FS) samples taken in Hanoi urban area had COD values ranging from 2.83 g/L to 83.83 g/L,TN values from 0.18 g/L to 3.95 g/L, and VS/TS ratio from 47.5 % to 87.7 %. Sewage sludge (SS) samples taken from sewage treatment plants in Hanoi had COD values ranging from 2.22 g/L to 24.97 g/L, TN from 0.16 g/L to 1.24 g/L, VS/TS ratio from 53.5 % to 69.5 %. Bio-methane potential (BMP) tests at mesophilic anaerobic condition (35 oC) provided results of methane production from FS, primary sewage sludge (PSS), waste activated sludge (WAS1 and WAS2) and mixture of primary and secondary sewage sludge at sludge thickener (WAS) as much as 242.3 NmL/gVS, 310.5 NmL/gVS, 294 NmL/gVS, 228.2 NmL/gVS and 282.3 NmL/gVS, respectively. Co-digestion of FS and WAS at different mixing ratios provided from 269.3 NmL to 294.8 NmL CH4 per gram of fed substrate VS. The values of methane yield have shown promising sludge-to-energy option with FS-SS co-digestion. FS-SS co-digestion in anaerobic digesters built at municipal sewage treatment plants which are often working under capacity provides chance to combat with FS and SS challenges, utilizing infrastructure facilities efficiently.

DEVELOPMENT OF A COMPUTER PROGRAMME FOR THE DESIGN OF MUNICIPAL WASTEWATER TREATMENT FACILITIES Part 6: Sludge Thickening and Blending Facility

The first sludge proc essing unit in a municipal wastewater treatment plant is sludge blending tank and sludge thickener before the sludge flow into sludge stabilization unit. A computer programme was developed using FORTRAN to design sludge blendin g tank and sludge thickening facility. The design include determining the size and hydraulic profile in the sludge thickener and in sludge blending tank. The influent and effluent structure is also designed using the same method in the secondary clarifier. The' input data to this computer programme is mainly the quantity of sludge effluent from the primary sedimentation bas ins and from the secondary or final clarifiers. These values are computed in a separate subroutine which analyze the material mass balance in the treatment plant. The thickened sludge withdrawal rate and the effluent quality from the sludge thickener are also computed . The results are easy to interpret and automatically appear on the computer screen or in an output file.

Empirical Study on Applicability of Phosphorus Recovery Process in Wastewater Treatment Plant

In this study, we have made the annual total phosphorus (TP) mass balance diagrams for I wastewater treatment plant by utilizing the data of flow rate and TP of each process and tried to choose the optimum unit process empirically for phosphorus recovery. For the applicability evaluation, we have suggested several quantitative indices of flow rate, TP concentration, TP load and SS. Based on the analyses of TP mass balance, it became clear for reducing TP load of the wastewater treatment plant that it is efficient to recover phosphorus from the side stream in which the amount of flow rate is just 1/16, but TP concentration and load are 78 and 4.8 times larger than those of the influent of the plant. After the detailed applicability evaluation for the side stream, it could be concluded that the unit process of waste activated sludge thickener supernatant or dehydration filtrate are appropriate. Meanwhile, we did fundamental experiments utilizing the dewatering filtrate with TP concentration of 141.5 mg/L. After adjusting pH 10 and Ca2+ concentration 250, 500, 1000 mg/L, it was stirred slowly. As a result, the PO4-P and TP removal efficiencies were above 95 percent; the results of the experiment imply the applicability of phosphorus recovery process in a wastewater treatment plant strongly. Key words: Side Stream, Phosphorus Recovery, Hydroxyapatite, Phosphorus Mass Balance, Wastewater Treatment Plant

Characteristics of methane and nitrous oxide emissions from the wastewater treatment plant

The nitrous oxide (N2O) and methane (CH4) emissions were measured from a municipal wastewater treatment plant (WWTP) using a flux chamber to determine the emission factors. The WWTP treats sewage using both the activated-sludge treatment and anaerobic/anoxic/aerobic (A2O) methods. Measurements were performed in the first settling, aeration, and secondary settling basins, as well as in the sludge thickener, sludge digestion tank, and A2O basins. The total emission factors of N2O and CH4 from the activated-sludge treatment were 1.256gN2O/kg total nitrogen (TN) and 3.734gCH4/kg biochemical oxygen demand (BOD5), respectively. Those of the advanced treatment (A2O) were 1.605gN2O/kg TN and 4.022gCH4/kgBOD5, respectively. These values are applicable as basic data to estimate greenhouse gas emissions.

농축조 상징액을 대상으로한 실험실 규모 아질산화 반응조 분석

Nitrogen is one of main causes to induce eutrophication of water system and one of contaminants that must be treated for protection of water system. In this study, it was intended to identify a method to increase operation efficiency of municipal wastewater treatment plant (MWTP) by treating high concentration nitrogen. A laboratory scale reactor was operated by using sludge thickener supernatant in the MWTP. During operation of the laboratory scale reactor, it was intended to induce stable nitritation and analyze effects of related operation factors. As results, it was shown that the nitiritation could be induced artificially through control of retention time and sections where the stable nitiritation was induced were identified also. In particular, highly efficient nitrite conversion efficiency near 90% was identified in condition of 1 day retention time. Especially, it was shown that ammonium nitrogen load affected ammonium nitrogen removal efficiency and nitrite conversion efficiency. In the condition of high ammonium nitrogen load, the nitrite conversion efficiency and the ammonium nitrogen removal efficiency decreased. On the contrary in the condition of low ammonium nitrogen load, it was found that the nitrite conversion efficiency decreased. It means that control of ammonium nitrogen concentration and its retention time is needed for the nitritation. It is considered that for the sewage containing high load nitrogen in sludge treatment process as like the sludge thickener supernatant, the nitritation can be applied, which can be suggested as a modification method of MWTP.

정수장 슬러지 농축조 배출수의 망간 농도에 미치는 pH의 영향

정수공정 중에 응집된 망간은 슬러지 농축조에 체류하는 동안 재용출 되어 배출수의 망간 허용기준치를 초과하는 문제가 발생되고 있다. 본 연구에서는 정수공정 중에 슬러지 농축조 배출수의 pH를 조정함으로써 망간 농도에 미치는 pH의 영향에 대하여 연구하였다. 초기 pH 6.1에서는 응집된 슬러지로부터 망간이 재용출 되어 청정지역 배출 기준인 2mg/L를 초과하였으나 NaOH, KOH, CaO, <TEX>$Ca(OH)_2$</TEX>, <TEX>$CaCO_3$</TEX> 등 알칼리 물질을 이용하여 pH를 상승시켰을 경우 망간 농도를 청정지역 배출 기준 이하로 낮출 수 있었다. 또한 알칼리성 물질로서 석회석 광산에서 선별과정 중 발생하는 폐석회석을 이용하여 정수장 슬러지의 망간 재용출을 억제할 수 있는 가능성을 확인하였다. Manganese in sludge precipitated during water treatment might be soluble again in effluent from sludge thickener. If that happens, the manganese concentration of effluent from water treatment plant will exceed the limit for clean reservation. In this study the influence of pH on Mn concentration of effluent from sludge thickener of water treatment plant was investigated. When the pHs of sludge solutions increased with alkaline materials such as NaOH, KOH, CaO, <TEX>$Ca(OH)_2$</TEX>, <TEX>$CaCO_3$</TEX>, the Mn concentrations of sludge solutions decreased under the limit. The Mn concentration of effluent from sludge thickener could be controlled with waste limestones from beneficiation process at limestone mine as an alkaline material.

Improvement of nitrification in winter using dewatering water

The reject water from the bioreactor of a domestic sewage treatment plant consists of supernatants of the anaerobic digestion tank and sludge thickener and dewatering water, which account for about 1–3% of the wastewater influent flow rate. Among these, dewatering water is very beneficial as it makes nitrification bacteria the dominant micro-organisms due to their higher nitrogen concentration and alkalinity, and their lower suspended solid, compared to those of the digester supernatant. This study was designed to improve the efficiency of nitrification in winter. Toward this end, the number of nitrifying micro-organisms was increased using dewatering water in the nitrification tank, and then they were introduced into the aeration tank to investigate the nitrification trends before and after the introduction. A comparative experiment was conducted at 12.5°C with an aeration tank having a capacity of 20 m3/d. The results showed average NH4+–N concentrations of the treated water of 8.5 and 18.4 mg/L in the pilot plant and the sewage treatment plant, respectively, and average NO3−–N concentrations of the treated water were 24.3 and 6.0 mg/L, respectively, which revealed nitrification improvement with the injection of dewatering water. The results of the microbiological analysis showed 3.27% total nitrification bacteria in the aeration tank of the pilot plant and 1.28% in that of the wastewater treatment plant, which indicate that the winter nitrification improved in the pilot plant.