Multi-soil-layering Systems Research Articles

Progress in Multi-Soil-Layering Systems for Wastewater Treatment

The use of decentralized wastewater treatment technologies is a reasonable solution for rural areas. As a decentralized treatment technology, the multi-soil-layering (MSL) system has recently drawn an increasing amount of attention owing to its merits, such as a high hydraulic load rate, small land area occupation, low probability of clogging, low investment, and low operation cost. This review summarizes the progress in MSL systems in the past decade, focusing on the directions of efforts for system optimization, the latest applications of MSL systems to various wastewater treatments, and the integration of MSL with other technologies. The great application potential of MSL systems is illustrated, and future research directions regarding better application of MSL systems are provided.

Eco-friendly management of harmful cyanobacterial blooms in eutrophic lakes through vertical flow multi-soil-layering technology

Eutrophication has led to the widespread occurrence of cyanobacterial blooms. Toxic cyanobacterial blooms with high concentrations of microcystins (MCs) have been identified in the Lalla Takerkoust reservoir in Morocco. The objective of this study was to evaluate the efficiency of the Multi-Soil-Layering (MSL) ecotechnology in removing natural cyanobacterial blooms from the lake. Two MSL pilots were used in rectangular glass tanks (60 × 10 × 70 cm). They consisted of permeable layers (PLs) made of pozzolan and a soil mixture layer (SML) containing local soil, ferrous metal, charcoal and sawdust. The main difference between the two systems was the type of local soil used: sandy soil for MSL1 and clayey soil for MSL2. Both MSL pilots effectively reduced cyanobacterial cell concentrations in the treated water to very low levels (0.09 and 0.001 cells/mL). MSL1 showed a gradual improvement in MC removal from 52 % to 99 %, while MSL2 started higher at 90 % but dropped to 54% before reaching 86%. Both MSL systems significantly reduced organic matter levels (97.2 % for MSL1 and 95.8 % for MSL2). Both MSLs were shown to be effective in removing cyanobacteria, MCs, and organic matter with comparable performance.

Disentangling microbial coupled fillers mechanisms for the permeable layer optimization process in multi-soil-layering systems

The multi-soil-layering (MSL) systems is an emerging solution for environmentally-friendly and cost-effective treatment of decentralized rural domestic wastewater. However, the role of the seemingly simple permeable layer has been overlooked, potentially holding the breakthroughs or directions to addressing suboptimal nitrogen removal performance in MSL systems. In this paper, the mechanism among diverse substrates (zeolite, green zeolite and biological ceramsite) coupled microorganisms in different systems (activated bacterial powder and activated sludge) for rural domestic wastewater purification was investigated. The removal efficiencies performed by zeolite coupled with microorganisms within 3 days were 93.8% for COD, 97.1% for TP, and 98.8% for NH4+-N. Notably, activated sludge showed better nitrification and comprehensive performance than specialized nitrifying bacteria powder. Zeolite attained an impressive 89.4% NH4+-N desorption efficiency, with a substantive fraction of NH4+-N manifesting as exchanged ammonium. High-throughput 16S rRNA gene sequencing revealed that aerobic and parthenogenetic anaerobic bacteria dominated the reactor, with anaerobic bacteria conspicuously absent. And the heterotrophic nitrification-aerobic denitrification (HN-AD) process was significant, with the presence of denitrifying phosphorus-accumulating organisms (DPAOs) for simultaneous nitrogen and phosphorus removal. This study not only raises awareness about the importance of the permeable layer and enhances comprehension of the HN-AD mechanism in MSL systems, but also provides valuable insights for optimizing MSL system construction, operation, and rural domestic wastewater treatment.

Enhanced Treatment of Decentralized Domestic Sewage Using Gravity-Flow Multi-Soil-Layering Systems Coupled with Iron-Carbon Microelectrolysis

Soil-based decentralized treatment technology has become increasingly popular as an ideal solution for water pollution control in rural areas. It is very necessary to optimize the removal mechanisms and performance of such technologies on rural domestic sewage treatment. This was the first study of a gravity-flow multi-soil-layering (MSL) system coupled with iron-carbon microelectrolysis (ICM). Influent COD/TN (C/N) ratio and bottommost soil mixture block (SMB) submersion were selected as the operating factors relevant to the ICM in MSL systems. Such two key factors were investigated in the factorial experiment. The removal efficiencies of COD, TP, NH3-N, NO3−-N, and TN could be reached up to 96.3, 100, 95.4, 93.8, and 79.6%, respectively. Different levels of factors could comprehensively drive the performance variation. The factorial analysis indicated that the bottommost SMB submersion had the most significant and dominant negative effects on aerobic processes. The ideal TP removal attributed to the presence of the bottommost SMB submersion. It played the dominant role for the bottommost SMB submersion in facilitating an electrochemical reaction through the ICM. Zero-valent iron or ferrous ions could be transformed to final ferric ions more efficiently during the period of the ICM reactions. The ICM could promote the capability of a SMB for removing nutrients in sewage, especially provide electron donors to denitrifying bacteria in MSL systems. However, there were non-significant effects of the influent C/N ratio on the removal performance of MSL systems. This study can help enrich the pollutant removal mechanisms in MSL systems.

Multi-Soil-Layering Technology: A New Approach to Remove Microcystis aeruginosa and Microcystins from Water

Eutrophication of surface waters caused by toxic cyanobacteria such as Microcystis aeruginosa leads to the release of secondary metabolites called Microcystins (MCs), which are heptapeptides with adverse effects on soil microbiota, plants, animals, and human health. Therefore, to avoid succumbing to the negative effects of these cyanotoxins, various remediation approaches have been considered. These techniques involve expensive physico-chemical processes because of the specialized equipment and facilities required. Thus, implementing eco-technologies capable of handling this problem has become necessary. Indeed, multi-soil-layering (MSL) technology can essentially meet this requirement. This system requires little space, needs simple maintenance, and has energy-free operation and high durability (20 years). The performance of the system is such that it can remove 1.16 to 4.47 log10 units of fecal contamination from the water, 98% of suspended solids (SS), 92% of biological oxygen demand (BOD), 98% of chemical oxygen demand (COD), 92% of total nitrogen (TN), and 100% of total phosphorus (TP). The only reported use of the system to remove cyanotoxins has shown a 99% removal rate of MC-LR. However, the mechanisms involved in removing this toxin from the water are not fully understood. This paper proposes reviewing the principal methods employed in conventional water treatment and other technologies to eliminate MCs from the water. We also describe the principles of operation of MSL systems and compare the performance of this technology with others, highlighting some advantages of this technology in removing MCs. Overall, the combination of multiple processes (physico-chemical and biological) makes MSL technology a good choice of cyanobacterial contamination treatment system that is applicable in real-life conditions, especially in rural areas.

Exploring the decentralized treatment of sulfamethoxazole-contained poultry wastewater through vertical-flow multi-soil-layering systems in rural communities

Sulfamethoxazole (SMX) is the most widely distributed sulfonamide antibiotics detected in decentralized poultry wastewater in rural communities. As an economically-feasible and eco-friendly technology for decentralized wastewater treatment in rural areas, vertical-flow multi-soil-layering (MSL) system was promising to mitigate the ecological and human health risks from SMX in such areas. The treatment of SMX-contained poultry wastewater by using MSL systems was investigated for the first time, and the main and interactive effects of related multiple variables on system performance were explored through factorial analysis, including material of permeable layer, concentration of SMX, and pH of influent. Results indicated that SMX concentration and pH of influent showed significantly negative effects on SMX removal. Medical stone used in MSL systems with larger surface area could intensify the SMX removal compared to anthracite. MSL systems showed stable performances on SMX removal with the best SMX removal efficiency more than 91%. A novel stepwise-cluster inference (SCI) model was developed for the first time to map the multivariate numeric relationships between state variables and SMX removal under discrete and nonlinear complexities. It was demonstrated that the effect of SMX in wastewater with high concentration was significant on the differentiation of soil bacteria composition in MSL systems based on microbial diversity analysis. These results can help better understand the mechanism of SMX removal in MSL systems from perspectives of factorial analysis, numeric modeling, and microbiological change.

Predicting the concentration of total coliforms in treated rural domestic wastewater by multi-soil-layering (MSL) technology using artificial neural networks

Many indicators are involved in monitoring water quality. For instance, the fecal indicator bacteria are extremely important to detect the water quality. For this purpose, to better predict the total coliforms at the outlet of a Multi-Soil-Layering (MSL) system designed to treat domestic wastewater in rural areas, a neural network model has been developed and compared with linear regression model. The data was collected from the raw and treated wastewater of a three MSL systems during a one-year period in rural village, in Al-Haouz Province, Morocco. Fifteen physicochemical and bacteriological variables have undergone feature selection to select the best ones for predicting the total coliforms concentration in the effluent of MSL system. Furthermore, 80% of the available dataset were used to train and optimize the neural model using repeated cross validation technique. The remaining part (20%) was used to test the developed model. The neural network indicated excellent results compared to the linear regression. The optimal model was a neural network with one hidden layer and 11 neurons, where the R2 was about 97%. The importance analysis of each predictor was established, and it was found that pH and total suspended solids had the greatest influence on the total coliforms removal.

Efficiency of Multi Soil Layering (MSL) System in A Household Scale of Wastewater Treatment Using Environmental Friendly Materials

Most community settlements in Indonesia do not have a household scale of a wastewater treatment plant. Fatal impacts on the environment and human health can occur at any time, including (a) causing environmental damage (disaster), (b) damaging beauty/aesthetics for the scenery will be unpleasant and foul-smelling, (c) polluting water bodies, and (d ) endangering health. The purpose of this study is to optimize the Multi Soil Layering (MSL) System to treat domestic wastewater (greywater) using environmentally friendly materials that are available in Indonesia. The research method used the MSL system with the first variation using a batch system with Hydraulic retention time (HRT) for 24 hours and the second variation using an intermittent system with 3, 6, 9 hours HRT. The results showed that the MSL system was able to eliminate COD well. The highest COD removal efficiency was 93.44% at 9 hours HRT, but the effluent quality did not meet the required quality standards. The development of MSL systems that produces an effluent quality that meets the quality standards needs to be studied further.

Comparative study about the performance of three types of modified natural treatment systems for rice noodle wastewater

In this study, three semi-pilot scale systems (vertical flow constructed wetland, multi-soil layering, and integrated hybrid systems) for treating real rice noodle wastewater were operated parallelly for the first time in a tropical climate at a loading rate of 50 L/(m2·d) for more than 7 months to determine the optimal conditions and to compare their treatment performance. The results demonstrated that these systems were appropriate for the removal of organics, suspended solids, and total coliform (Tcol). The highest reductions in chemical oxygen demand (CODCr, 73.2%), phosphorus (PO4-P, 54%), and Tcol (4.78 log MPN/100 mL inactivation) were obtained by the integrated hybrid system, while the highest removal efficiencies of ammonium (NH4-N, 60.64%) and suspended solids (80.49%) were achieved in the vertical-flow-constructed wetland and multi-soil layering systems respectively.

Evaluation of Long-Term Wastewater Treatment Performances in Multi-Soil-Layering Systems in Small Rural Communities

Multi-soil-layering (MSL) wastewater treatment systems consist of soil units (soil mixture blocks, SMB) arranged in a brick-like pattern surrounded by permeable layers of zeolite or alternating particles of homogeneous sizes that allow for a high hydraulic loading rate. This study evaluated the performances of MSL systems that have been operating for 17 to 20 years in small rural communities. Even though 20 years had passed since this system was installed, high organic matter treatment performance continued. Nitrogen removal was higher than with conventional soil systems. Two of the MSL systems continued to show high phosphorus removal performances, whereas in the third system, the adsorbing capacity was relatively low, requiring further investigation. Treatment performances were largely dependent upon the structure of the MSL systems. It appeared that improving the structure to enhance the contact efficiency between the wastewater and the soil in SMB was important for enhancing treatment performances. The combined use of existing wastewater treatment systems with the MSL system was effective for preventing environmental pollution over a long period.

Biophysiological and factorial analyses in the treatment of rural domestic wastewater using multi-soil-layering systems

Multi-soil-layering (MSL) system was developed as an attractive alternative to traditional land-based treatment techniques. Within MSL system, the environmental cleanup capability of soil is maximized, while the soil microbial communities may also change during operation. This study aimed to reveal the nature of biophysiological changes in MSL systems during operation. The species diversity in soil mixture blocks was analyzed using Illumina HiSeq sequencing of the 16S rRNA gene. The interactive effects of operating factors on species richness, community diversity and bacteria abundance correlated with COD, N and P removal were revealed through factorial analysis. The results indicated the main factors, aeration, bottom submersion and microbial amendment, had different significant effects on microbial responses. The surface area and porosity of zeolites in permeable layers decreased due to the absorption of extracellular polymeric substances. The findings were applied for the design and building of a full-size MSL system in field and satisfied removal efficiency was achieved. The results of this study can help better understand the mechanisms of pollutant reduction within MSL systems from microbial insights. It will have important implications for developing appropriate strategies for operating MSL systems with high efficiency and less risks.

Treatment of rural domestic wastewater using multi-soil-layering systems: Performance evaluation, factorial analysis and numerical modeling

The discharge of wastewater in rural areas without effective treatment may result in contamination of surrounding surface water and groundwater resources. This study explored the wastewater treatment performance of multi-soil-layering (MSL) systems through interactive factorial analysis. MSL systems showed good performances under various operating conditions. The COD and BOD5 removal rates in MSL systems could reach 98.53 and 93.66%, respectively. The performances of MSL systems in TP removal stayed at high levels ranged from 97.97 to 100% throughout the experiments. The NH4+ − N removal rates of the well performed MSL systems reached highest levels ranging from 89.96 to 100%. The TN removal rates of aerated MSL systems ranged from 51.11 to 64.44% after 72 days of operation. The independent effects of bottom submersion, microbial amendment and aeration, as well as most interactions were significant. The performance of MSL systems was mainly affected by bottom submersion and aeration as well as their interactions. Aeration was the most positive factor for the removal of organic matter, TP and NH4+ − N. However, oxygenated environment was unfavorable for NO3− − N removal. In the submerged area with limited oxygen, the microbial transformation of NO3− − N still occurred. A stepwise-cluster inference model was developed for tackling the multivariate nonlinear relationships in contaminant removal processes. The results can help obtain a better understanding of the complicated processes among contaminant removal in MSL systems.

Performance of single-pass and by-pass multi-step multi-soil-layering systems for low-(C/N)-ratio polluted river water treatment

Two kinds of hybrid two-step multi-soil-layering (MSL) systems loaded with different filter medias (zeolite-ceramsite MSL-1 and ceramsite-red clay MSL-2) were set-up for the low-(C/N)-ratio polluted river water treatment. A long-term pollutant removal performance of these two kinds of MSL systems was evaluated for 214 days. By-pass was employed in MSL systems to evaluate its effect on nitrogen removal enhancement. Zeolite-ceramsite single-pass MSL-1 system owns outstanding ammonia removal capability (24 g NH4+-Nm−2d−1), 3 times higher than MSL-2 without zeolite under low aeration rate condition (0.8 × 104 L m−2.h−1). Aeration rate up to 1.6 × 104 L m−2.h−1 well satisfied the requirement of complete nitrification in first unit of both two MSLs. However, weak denitrification in second unit was commonly observed. By-pass of 50% influent into second unit can improve about 20% TN removal rate for both MSL-1 and MSL-2. Complete nitrification and denitrification was achieved in by-pass MSL systems after addition of carbon source with the resulting C/N ratio up to 2.5. The characters of biofilms distributed in different sections inside MSL-1 system well illustrated the nitrogen removal mechanism inside MSL systems. Two kinds of MSLs are both promising as an appealing nitrifying biofilm reactor. Recirculation can be considered further for by-pass MSL-2 system to ensure a complete ammonia removal.

Wastewater Treatment Plant Performance Inside Multi-Soil-Layering System

Wastewater effluent disposal is a challenge in Moroccan rural area. Wastewater treatment is the only suitable solution to overcome these environmental constraints. Technology such as Multi-Soil-Layering (MSL) system is one of the most appropriate solution for the treatment of wastewater for small communities in rural areas. The MSL system overcomes many of the deficiencies of conventional soil treatment systems such as large land requirement clogging and low Hydraulic Loading Rate (HLR). The MSL systems are composed of Soil Mixture Blocks (SMB) arranged in a brick-like pattern and surrounded by Permeable Layers (PL). To investigate the efficiency of MSL systems in relation to HLR differences and the fluctuations in the wastewater contamination levels, three MSL pilot plants were alimented continuously by domestic wastewater, were constructed in three 36×30×65 cm plastic boxes, with different HLR of 250, 500 and 1000 l/m2/day. The main removal rates of Biochemical Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD) were higher at higher HLR. However, the kinetic rate constant of the MSL process implemented under Moroccan conditions is 130 d-1 at 25°C.

Clarification of water movement properties in a multi-soil-layering system

In multi-soil-layering (MSL) systems, the effect of the materials and structural differences on the wastewater treatment performance and clogging mechanisms are not fully understood because of insufficient quantitative evaluations of water movement properties inside the system. In the present study, water movement properties were examined using laboratory-scale MSL systems consisting of one to six soil mixture layers (SML). The aims were to determine (1) changes in water movement characteristics inside the systems by varying the hydraulic loading rate (HLR), (2) the relationship between the number of inflow points and water movement characteristics, and (3) water movement characteristics and clogging mechanisms under wastewater treatment conditions.As the HLR increased, the flow rates in the SML increased linearly, followed by a slight decline in the rate of increase, whereas flow rates in the permeable layers (PL) between the SML (PLb) increased exponentially except in the system with one layer. Water movement inside the systems with one inflow point inclined toward the central part of the system compared to that with three inflow points. Under wastewater treatment conditions, flow rates in the first SML decreased to 437 L m−2 day−1 from 1433 L m−2 day−1 in three days after applying wastewater. However, as the number of layers increased, high flow rates in the SML were maintained for longer periods. In the first to third SML, a decreasing trend of oxidation–reduction potential (Eh) values was correlated with a decrease in flow rates. Partial clogging in the first PLb was associated with Eh values in the PL of the upper part beginning to decrease. The study indicated that establishment of an optimum structure, materials, and aeration was required to maintain a proper level of permeability and anaerobic conditions inside the SML, which would facilitate simultaneous removal of organic matter, nitrogen and phosphorus.

Quantitative evaluation of treatment processes and mechanisms of organic matter, phosphorus, and nitrogen removal in a multi-soil-layering system

The water treatment performance of multi-soil-layering (MSL) systems has been mainly evaluated by measuring differences in the quality of wastewater and treated water. Changes in water quality inside the system have not been assessed together with the water movement. In this study, therefore, quantitative evaluation of the treatment processes inside the MSL system was conducted using laboratory-scale MSL systems, which were set up in 10 cm (depth) × 50 cm (width) × 23–73 cm (height) acrylic boxes enclosing “soil mixture blocks” alternating with permeable zeolite layers. Six MSL systems consisting of one to six soil mixture layers (SML) were constructed, and treated water from the SML and the permeable layers between the SML (PLb) was collected separately at the bottom of each system. In order to determine the treatment processes inside the system, wastewater, with mean concentrations of biological oxygen demand (BOD) 28.1 mg L−1, chemical oxygen demand (COD) 65.7 mg L−1, total nitrogen 9.8 mg L−1, total phosphorus 1.0 mg L−1, was introduced into the system at a hydraulic loading rate of 1000 L m−2 day−1. Concentrations of both BOD and COD in the SML were lower than those in the PLb. As the flow rate in the SML decreased and the rate in the PLb increased, concentrations increased in the PLb in each system. Although the removal rate of BOD always exceeded 80% in the systems with more than three layers, six layers were required for COD to be reduced to the same extent as BOD. Phosphorus concentrations were also lower in the SML than in the PLb due to the adsorption of phosphorus by the soil and mixed iron particles. Therefore, phosphorus removal efficiency was strongly influenced by flow rate in the SML. In this study, the ammonium adsorption and nitrification were almost completed down to the third layer of the MSL system. However, the removal of nitrogen did not proceed much below the fourth layer due to low denitrification efficiency.

Effect of aeration and material composition in soil mixture block on the removal of colored substances and chemical oxygen demand in livestock wastewater using multi-soil-layering systems

To investigate the efficiency of multi-soil-layering (MSL) systems on the removal of colored substances and chemical oxygen demand (COD) from livestock wastewater, four MSL systems with different soil mixture block (SMB) compositions were constructed in four 50 cm × 10 cm × 68 cm acrylic boxes. Livestock wastewater (diluted 10-fold) with an absorbance of 0.9215 at a wavelength of 406 nm and a COD concentration of approximately 3,000 mg L−1 was applied to the systems at a hydraulic loading rate (HLR) of 250 L m−2 day−1. Aeration pipes were set in the water permeable layers (PL) in MSL 1–3 and in the SMB layers in MSL 4. The results showed that MSL systems could keep mean decolorization rates of 60.7–67.1% and COD removal rates of 48.8–58.0% for 6 weeks of operation. The different aeration pipe positions did not have any significant influence on the removal efficiency of the systems. However, an increase in aeration intensity from 1,000 to 2,000 L min−1 per system (27.4–54.8 L min−1 L−1) increased decolorization rates by 3.0–12.1%. For COD removal, both an increase in aeration intensity and temperature enhanced the removal rates by 23.0–43.3%. The addition of sawdust and iron into the SMB of MSL 1 improved the system's decolorization rate by 9.1% and COD removal rate by 12.0% compared with MSL 2 during the fifth and sixth months of operation. Interruption of MSL systems for 1 month could recover the decolorization and COD removal rates to over 50% and 80%, respectively.

A comparative study of permeable layer materials and aeration regime on efficiency of multi-soil-layering system for domestic wastewater treatment in Thailand

Multi-soil-layering (MSL) system was designed for purifying domestic wastewater and for treating polluted river water. MSL system is typically comprised of layers of soil mixture blocks alternating with permeable layers. The permeable layer has roles of preventing clogging and to increasing the efficiency of infiltration of wastewater through the soil mixture blocks. In this study, the comparative efficiency of five MSL systems as a function of five permeable layer materials (zeolite, zeolitized perlite, perlite, gravel, and charcoal) was investigated. The MSL systems were constructed in 15 × 50 × 100 cm boxes where the soil mixture blocks contained sandy clay soil, kenaf + corncob, and iron scraps at a ratio of 6 : 1 : 1 by weight, respectively, and filled up in alternation with the permeable layer. The results indicated that all the MSL systems at loading rates of 96–346 L m−2 d−1 under nonaerated conditions were able to reduce the levels of COD (342–1,231 mg L−1), BOD5 (201–802 mg L−1), and soluble reactive phosphorus (SRP) (3.5–10.1 mg P L−1) at percentages of 79.0–98.1, 80.0–99.6, and 97.1–100%, respectively. The zeolite and the charcoal-based MSL systems under a 96–346 L m−2 d−1 loading rate effectively reduced the level of TN (41.4–65.5 mg N L−1) at percentages of 79.0–92.1 and 30.7–88.9%, respectively. In terms of prevention of clogging, the charcoal-based MSL system was the most effective, followed by the gravel and zeolite-based MSL. The apparent efficiency of pollutant removal, for zeolitized perlite, perlite, and gravel-based MSL systems was low. With an on-off aeration operation, the efficiency of the MSL systems in the reduction of the levels of COD, BOD5 , and SRP (hereafter reference to as “removal”) was significantly enhanced. Overall, the zeolite-based MSL system seemed to be more effective than the other MSL systems. However, if optimum aeration could be obtained, the removal efficiency of charcoal-based MSL system might be improved. Aeration at a rate of 64,000 L m−3 d−1 for 1 week alternating with 2 weeks of nonaeration enhanced the removal of COD, BOD5 , and SRP but not that of TN.

Effect of organic components and aeration regimes on the efficiency of a multi-soil-layering system for domestic wastewater treatment

Multi-soil-layering (MSL) system can be applied to wastewater treatment. The component of an MSL system can be varied as a function of site-specific availability of materials. This study investigates the comparative efficiency of five MSL systems as a function of alternative organic materials (Japanese sawdust, Thai sawdust, rice straw, kenaf, and corncob). The MSL systems were set up in 15 × 50 × 100 cm boxes consisting of “soil mixture blocks” alternated with a zeolite layer. The February–May 1999 results indicated that all the MSL systems under a non-aeration regime effectively reduced the biochemical oxygen demand (BOD5) and removed soluble reactive phosphorus (SRP) with percentages ranging from 88.0–99.8 and 92.5–100, respectively. From January to September 2000 when an on-off aeration regime was adopted, the MSL treatments comprising rice straw, kenaf, and corncob continued to effectively reduce BOD5 and remove SRP. On the other hand, the efficiency of Japanese sawdust and Thai sawdust MSL treatments in reducing BOD5 and removing SRP gradually decreased. Fine particles and slowly decomposable characteristics of Thai sawdust and Japanese sawdust induced compaction and subsequent clogging. Therefore, rice straw, kenaf, and corncob were found to be more appropriate than Thai sawdust and Japanese sawdust for use as components of the MSL systems. Aeration at a rate of 64,000 L m−3 d−1 for 1 week enhanced BOD5 reduction and SRP removal, especially, when clogging was observed. However, aeration at this rate reduced the TN removal efficiency of the MSL system due to the inhibition of denitrification, excessive nitrification as well as the discharge of stored NH4 +-N.

多段土壌層法による生物系排水処理 モデル装置の送気位置の違いによる処理能力の比較

The effects of various positions of aeration in Multi-Soil-Layering (MSL) method of bio-genic waste water treatment were investigated. Porous aeration pipes were installed in upper, middle, and lower positions in model MSL systems. Each model MSL packed in 10X50X60cm sized acrylic box. Air was supplied at the rate of 48000 l·m-3·d-1 through the porous pipes installed at various positions. Loading rate of waste water was 288 l·m-2·d-1. In the upper position of aeration, clogging was prevented and nitrogen removal was efficient. But efficiency of aeration was low for high level of removal of COD·BOD and T-P, because air leaked from surface of the system. In the middle position of aeration, the efficiency of T-P removal and decomposition of organic matter were high because of the efficient aeration to create relatively large aerobic parts in the MSL. But nitrogen removal was low. Because of nitrate was leaching. It was thought that anaerobic parts were too small to efficient denitrification. In the lower position of aeration, clogging was happened at the early stages of treatments. Fe(II) and Mn(II) were oxidized efficiently to prevent the solubilization. COD·BOD of final effluent water was also low. Based on this study, if only one aeration position has to be selected, the appropriate aeration position was considered to be the position between the first and second of soil layers of MSL. This aeration position may prevent clogging effectively. Large aerobic condition may contribute to efficient phosphorus and organic matter removals. Nitrogen removal may also be enhanced because of nitrification of the upper position and denitrification of the lower position.However, since each upper, middle, and lower position showed different efficiency characteristics on treatments, the positioning of aeration and the operational condition should be selected depending on the given target of the treatment, including the combinations of the two positions, upper/lower, upper/middle, and middle/lower.