Amit Kumar Maharjan | University of Yamanashi (original) (raw)

Papers by Amit Kumar Maharjan

Industrial and Domestic Waste Management, Dec 20, 2021

The elevation of waste generation subsequent to population growth has become a severe environment... more The elevation of waste generation subsequent to population growth has become a severe environmental topic in Malaysia. Since most of the waste is being dumped into a landfill, the open dumpsite, or unsanitary landfills which are not constructed with proper engineering plan, severe impacts on the environment result. The energy demand in Malaysia increased with the growing population, but reliance on fossil fuels to generate electricity has created another greenhouse gas contributor. Alternatively, waste-to-energy technology solves the problem of increasing waste by converting the waste to a renewable energy source. Malaysia has moved towards landfill gas recovery system and incineration for waste energy recovery. The recovery system and refuse-derived fuel plant achieved expectation; however, the incineration plants have failed due to the opposition of the public, lack of funding and technician expertise, and other technical issues. The solid waste management practices lacking separation and recycling sources, become an obstacle for development. The government puts effort into solving the current issue by promoting recycling in the public, enforcing the legislation, and approaching new technologies for better solid waste management practice in the future. This paper aims to discuss the application of energy recovery from municipal solid waste in Malaysia.

Journal of Water and Environment Technology, 2021

Ammonium (NH 4 +) contamination makes groundwater undrinkable. The dropping nitrification unit, a... more Ammonium (NH 4 +) contamination makes groundwater undrinkable. The dropping nitrification unit, a simple and low-cost biological unit, has been found to be effective for NH 4 +-removal from contaminated groundwater at a near-neutral pH. However, the pH of groundwater varies widely and is highly alkaline (pH 8.7−10) in some areas of the world, which could negatively affect the biological nitrification process. The objectives of this study were to investigate the NH 4 +-removal from alkaline groundwater using dropping nitrification units with sponge or biofringe material, compare their removal efficiencies, and characterize the effect of alkaline groundwater on the growth and activity of nitrifying bacteria. Synthetic alkaline groundwater (50 mg-NH 4 +-N L −1 ; pH 9.4 ± 0.1) was dropped from the top of 1-m long hanging units at 3 mL min −1 for 56 days. The NH 4 +-removal efficiency of sponge units (> 88%) was significantly higher than that of biofringe units (56−89%). The abundance of amoA gene of ammonia-oxidizing bacteria increased significantly over 56 days and was significantly higher in sponge units than in biofringe units, resulting in higher NH 4 +-removal in sponge units than that in biofringe units. This study demonstrated that dropping nitrification units can be used effectively for NH 4 +-removal from groundwater having a neutral to alkaline pH.

Water, May 7, 2020

Constructed wetlands (CWs) are an effective technology to remove organic compounds and nitrogen (... more Constructed wetlands (CWs) are an effective technology to remove organic compounds and nitrogen (N) from wastewaters and contaminated environmental waters. However, the feasibility of CWs for ammonium-N (NH 4 +-N)-contaminated groundwater treatment is unclear. In this study, zeolite-based laboratory-scale CW was operated as a tidal flow CW with a cycle consisting of 21-h flooded and 3-h rest, and used to treat NH 4 +-N (30 mg L −1) contaminated groundwater. In addition to NH 4 +-N, nitrite (NO 2 −-N) and nitrate (NO 3 −-N) were also not detected in the effluents from the tidal flow CW. The N removal constant remained high for a longer period of time compared to the continuous flow CW. The higher and more sustainable N removal of the tidal flow CW was due to the in-situ biological regeneration of zeolite NH 4 +-N adsorption capacity. Vegetation of common reeds in tidal flow zeolite-based CW enhanced nitrification and heterotrophic denitrification activities, and increased the functional genes of nitrification (AOB-amoA and nxrA) and denitrification (narG, nirK, nirS, and nosZ) by 2-3 orders of magnitude, compared to CW without vegetation. The results suggest that the combination of zeolite substrate, tidal flow, and vegetation is key for the highly efficient and sustainable N removal from NH 4 +-N contaminated groundwater.

Water Science & Technology: Water Supply, Aug 17, 2021

A novel dropping nitrification-cotton-based denitrification reactor was developed for total nitro... more A novel dropping nitrification-cotton-based denitrification reactor was developed for total nitrogen (N) removal from ammonium (NH 4 þ)-contaminated groundwater. The nitrogen removal ability of the reactor was evaluated for 91 days. A 1 m-long dropping nitrification unit was fed with synthetic groundwater containing 30 mg-NH 4 þ-N/L at a flow rate of 2.16 L/d. The outlet of the dropping nitrification unit was connected to the cotton-based denitrification unit. The NH 4 þ present in the groundwater was completely oxidized (.90% nitrification efficiency) by nitrifying bacteria to nitrite (NO 2-) and nitrate (NO 3-) in the dropping nitrification unit. Subsequently, the generated NO 2 and NO 3 were denitrified (96%-98% denitrification efficiency) by denitrifying bacteria in the cotton-based denitrification unit under anoxic conditions. Organic carbons released from the cotton presumably acted as electron donors for heterotrophic denitrification. Nitrifying and denitrifying bacteria were colonized in higher abundance in the dropping nitrification and cotton-based denitrification units, respectively. The total N removal rate and efficiency of the dropping nitrification-cotton-based denitrification reactor for 91 days were 58.1-66.9 mg-N/d and 96%-98%, respectively. Therefore, the dropping nitrification-cotton-based denitrification reactor will be an efficient, sustainable, and promising option for total N removal from NH 4 þ-contaminated groundwater.

Journal of Water and Environment Technology

Tidal flow constructed wetlands (TFCWs) have been proposed as a new type of CW for enhanced waste... more Tidal flow constructed wetlands (TFCWs) have been proposed as a new type of CW for enhanced wastewater treatment. However, the characterization of TFCWs in the removal of organic carbon and nitrogen remains unclear. This study investigated the efficiencies and characteristics of lab-scale TFCWs in removing organic carbon and nitrogen from sewage; in particular, the dynamics of dissolved total organic carbon (DOC), nitrogen, and dissolved oxygen (DO) were observed. Pumice-and zeolite-TFCWs were prepared, which treated sewage at 21 h fill and 3 h rest cycles. Sewage was rapidly oxidized in these TFCWs after inflow. The experimental results showed that DOC was efficiently decreased by aerobic biodegradation with DO consumption. Additionally, NH 4 +-N was oxidized to NO 3 −-N by nitrification, the DO content decreased, and NO 3 −-N was removed by denitrification in the TFCWs. The processes of aerobic-anaerobic switching, organic carbon biodegradation, and nitrification-denitrification were observed in the TFCWs. During 128-days of operation, the pumiceand zeolite-TFCWs exhibited the DOC removal capacities of 4.2 and 4.3 g-DOC/m 2 /d, respectively, and total dissolved inorganic nitrogen removal capacities of 3.1 and 5.1 g-N/m 2 /d, respectively. These results revealed the higher organic carbon and nitrogen removal capacities and mechanisms of pumice-and zeolite-TFCWs treating sewage.

Tropical Aquatic and Soil Pollution, Oct 25, 2021

Heavy metal pollution in water resources has become a serious and hazardous environmental problem... more Heavy metal pollution in water resources has become a serious and hazardous environmental problem all over the world because of its non-biodegradability, emanating from multiple sources, easy accumulation, and biological toxicity. This research was carried out to study the level and distribution of heavy metals at different sampling locations (upstream, midstream, and downstream), at different depths (0.5 m and 1.5 m from surface water level), and during low tide and high tide conditions in the Miri River of Miri City in Malaysia. The river water samples were collected and analyzed for Ca, Mg, Cu, Fe, Mn, Ni, Pb, and Zn by flame atomic absorption spectrophotometer. The concentration of Ca was found to be the highest in the Miri River, followed by Mg and Fe, and with traces of Cu, Mn, Ni, Pb, and Zn. An increase in the concentration of heavy metals, such as Cu, Mg, and Ni, was observed while flowing from upstream to downstream of the Miri River. Concentrations of heavy metals, such as Ca, Mg, Cu, and Zn, were clearly lower at 1.5 m depth than at 0.5 m depth. High tides in the river decrease the concentration of heavy metals, such as Ca, Cu, Mn, and Ni, compared to low tides. From this research, it gets clear that using the Miri River water for domestic and recreational purposes, washing, and fishing is detrimental to human health and the environment.

Nepal Journal of Civil Engineering, 2021

With the rapid urbanization, the production of wastewater is increasing day by day. Direct discha... more With the rapid urbanization, the production of wastewater is increasing day by day. Direct discharge of wastewater in the water bodies/land causes environmental pollutions. Hence, treatment of the wastewater is must, prior to the disposal. Treatment of wastewater through constructed wetlands (CWs) require low cost, less energy consumption, easy construction, and simple operation/maintenance. So, CWs can be the better option for the developing countries such as Nepal. Main objective of the study was to determine the pollutant/nutrient removal abilities of total nitrogen (N), total phosphorous (P), potassium (K+), and biochemical oxygen demand (BOD) in the horizontal subsurface flow (HSSF) CW. The study was carried out in the HSSF CW having gravel as substrate material and common reed (narkat, phragmites karka) as macrophyte. The CW treated domestic wastewater at an average flow rate of 8.64 m3.d−1. The first order removal rate constants were 0.015 m−1 (0.200 d−1) for total N, 0.035 m...

Water Science and Technology

The partial denitrification and anammox (PDA) process has received attention for its ability to o... more The partial denitrification and anammox (PDA) process has received attention for its ability to optimize treatment of wastewater containing a low -N concentration. This study investigated the suitable operational conditions for -N accumulation by hydrogenotrophic denitrification (HD) in operation of a laboratory-scale moving bed biofilm reactor, for future application in the PDA process. -N accumulation was achieved by minimizing the H2 flow rate under optimized conditions (i.e., 15 mL/min H2 flow rate, 40 mg-N/L influent -N, 7.0 h hydraulic retention time, and 2 L working volume). Hydrogenophaga comprised 39.2% of the bacterial abundance after -N accumulated, indicating its contribution to the -N accumulation. In addition, an intermittent H2 supply maintained the -N accumulation rate (NAR) and maximized the nitrite accumulation efficiency (NAE). A H2 supply ratio of 0.7 (i.e., ON: 7 min, OFF: 3 min) was optimal, which induced increases in NAR, NAE, and the -N removal efficiency tha...

Journal of Water and Environment Technology, 2021

Ammonium (NH 4 +) contamination makes groundwater undrinkable. The dropping nitrification unit, a... more Ammonium (NH 4 +) contamination makes groundwater undrinkable. The dropping nitrification unit, a simple and low-cost biological unit, has been found to be effective for NH 4 +-removal from contaminated groundwater at a near-neutral pH. However, the pH of groundwater varies widely and is highly alkaline (pH 8.7−10) in some areas of the world, which could negatively affect the biological nitrification process. The objectives of this study were to investigate the NH 4 +-removal from alkaline groundwater using dropping nitrification units with sponge or biofringe material, compare their removal efficiencies, and characterize the effect of alkaline groundwater on the growth and activity of nitrifying bacteria. Synthetic alkaline groundwater (50 mg-NH 4 +-N L −1 ; pH 9.4 ± 0.1) was dropped from the top of 1-m long hanging units at 3 mL min −1 for 56 days. The NH 4 +-removal efficiency of sponge units (> 88%) was significantly higher than that of biofringe units (56−89%). The abundance of amoA gene of ammonia-oxidizing bacteria increased significantly over 56 days and was significantly higher in sponge units than in biofringe units, resulting in higher NH 4 +-removal in sponge units than that in biofringe units. This study demonstrated that dropping nitrification units can be used effectively for NH 4 +-removal from groundwater having a neutral to alkaline pH.

Industrial and Domestic Waste Management

The elevation of waste generation subsequent to population growth has become a severe environment... more The elevation of waste generation subsequent to population growth has become a severe environmental topic in Malaysia. Since most of the waste is being dumped into a landfill, the open dumpsite, or unsanitary landfills which are not constructed with proper engineering plan, severe impacts on the environment result. The energy demand in Malaysia increased with the growing population, but reliance on fossil fuels to generate electricity has created another greenhouse gas contributor. Alternatively, waste-to-energy technology solves the problem of increasing waste by converting the waste to a renewable energy source. Malaysia has moved towards landfill gas recovery system and incineration for waste energy recovery. The recovery system and refuse-derived fuel plant achieved expectation; however, the incineration plants have failed due to the opposition of the public, lack of funding and technician expertise, and other technical issues. The solid waste management practices lacking separa...

Water, 2021

High nitrate-nitrogen (NO3−–N) content is a typical feature of groundwater, which is the primary ... more High nitrate-nitrogen (NO3−–N) content is a typical feature of groundwater, which is the primary water source in the Kathmandu Valley, Nepal. Considering the Kathmandu Valley’s current problem of water scarcity, a user-friendly system for removing NO3−–N from groundwater is promptly desired. In this study, a simplified hydrogenotrophic denitrification (HD) reactor was developed for the Kathmandu Valley, and its effectiveness was evaluated by its ability to treat raw groundwater. The reactor operated for 157 days and showed stability and robustness. It had an average nitrogen removal efficiency of 80.9 ± 16.1%, and its nitrogen loading rate and nitrogen removal rate varied from 23.8 to 92.3 g–N/(m3∙d) and from 18.3 to 73.7 g–N/(m3∙d), respectively. Compared to previous HD reactors, this simplified HD reactor is a more user-friendly option for the Kathmandu Valley, as most of the materials used for the reactor were locally available and require less maintenance. The reactor is recomme...

Tropical Aquatic and Soil Pollution

Heavy metal pollution in water resources has become a serious and hazardous environmental problem... more Heavy metal pollution in water resources has become a serious and hazardous environmental problem all over the world because of its non-biodegradability, emanating from multiple sources, easy accumulation, and biological toxicity. This research was carried out to study the level and distribution of heavy metals at different sampling locations (upstream, midstream, and downstream), at different depths (0.5 m and 1.5 m from surface water level), and during low tide and high tide conditions in the Miri River of Miri City in Malaysia. The river water samples were collected and analyzed for Ca, Mg, Cu, Fe, Mn, Ni, Pb, and Zn by flame atomic absorption spectrophotometer. The concentration of Ca was found to be the highest in the Miri River, followed by Mg and Fe, and with traces of Cu, Mn, Ni, Pb, and Zn. An increase in the concentration of heavy metals, such as Cu, Mg, and Ni, was observed while flowing from upstream to downstream of the Miri River. Concentrations of heavy metals, such a...

Water

Constructed wetlands (CWs) are an effective technology to remove organic compounds and nitrogen (... more Constructed wetlands (CWs) are an effective technology to remove organic compounds and nitrogen (N) from wastewaters and contaminated environmental waters. However, the feasibility of CWs for ammonium-N (NH4+-N)-contaminated groundwater treatment is unclear. In this study, zeolite-based laboratory-scale CW was operated as a tidal flow CW with a cycle consisting of 21-h flooded and 3-h rest, and used to treat NH4+-N (30 mg L−1) contaminated groundwater. In addition to NH4+-N, nitrite (NO2−-N) and nitrate (NO3−-N) were also not detected in the effluents from the tidal flow CW. The N removal constant remained high for a longer period of time compared to the continuous flow CW. The higher and more sustainable N removal of the tidal flow CW was due to the in-situ biological regeneration of zeolite NH4+-N adsorption capacity. Vegetation of common reeds in tidal flow zeolite-based CW enhanced nitrification and heterotrophic denitrification activities, and increased the functional genes of ...

Water

A dropping nitrification reactor was proposed as a low-cost and energy-saving option for the remo... more A dropping nitrification reactor was proposed as a low-cost and energy-saving option for the removal of NH4+-N from contaminated groundwater. The objectives of this study were to investigate NH4+-N removal performance and the nitrogen removal pathway and to characterize the microbial communities in the reactor. Polyolefin sponge cubes (10 mm × 10 mm × 10 mm) were connected diagonally in a nylon thread to produce 1 m long dropping nitrification units. Synthetic groundwater containing 50 mg L−1 NH4+-N was added from the top of the hanging units at a flow rate of 4.32 L day−1 for 56 days. Nitrogen-oxidizing microorganisms in the reactor removed 50.8–68.7% of the NH4+-N in the groundwater, which was aerated with atmospheric oxygen as it flowed downwards through the sponge units. Nitrogen transformation and the functional bacteria contributing to it were stratified in the sponge units. Nitrosomonadales-like AOB predominated and transformed NH4+-N to NO2−-N in the upper part of the reacto...

Industrial and Domestic Waste Management, Dec 20, 2021

The elevation of waste generation subsequent to population growth has become a severe environment... more The elevation of waste generation subsequent to population growth has become a severe environmental topic in Malaysia. Since most of the waste is being dumped into a landfill, the open dumpsite, or unsanitary landfills which are not constructed with proper engineering plan, severe impacts on the environment result. The energy demand in Malaysia increased with the growing population, but reliance on fossil fuels to generate electricity has created another greenhouse gas contributor. Alternatively, waste-to-energy technology solves the problem of increasing waste by converting the waste to a renewable energy source. Malaysia has moved towards landfill gas recovery system and incineration for waste energy recovery. The recovery system and refuse-derived fuel plant achieved expectation; however, the incineration plants have failed due to the opposition of the public, lack of funding and technician expertise, and other technical issues. The solid waste management practices lacking separation and recycling sources, become an obstacle for development. The government puts effort into solving the current issue by promoting recycling in the public, enforcing the legislation, and approaching new technologies for better solid waste management practice in the future. This paper aims to discuss the application of energy recovery from municipal solid waste in Malaysia.

Journal of Water and Environment Technology, 2021

Ammonium (NH 4 +) contamination makes groundwater undrinkable. The dropping nitrification unit, a... more Ammonium (NH 4 +) contamination makes groundwater undrinkable. The dropping nitrification unit, a simple and low-cost biological unit, has been found to be effective for NH 4 +-removal from contaminated groundwater at a near-neutral pH. However, the pH of groundwater varies widely and is highly alkaline (pH 8.7−10) in some areas of the world, which could negatively affect the biological nitrification process. The objectives of this study were to investigate the NH 4 +-removal from alkaline groundwater using dropping nitrification units with sponge or biofringe material, compare their removal efficiencies, and characterize the effect of alkaline groundwater on the growth and activity of nitrifying bacteria. Synthetic alkaline groundwater (50 mg-NH 4 +-N L −1 ; pH 9.4 ± 0.1) was dropped from the top of 1-m long hanging units at 3 mL min −1 for 56 days. The NH 4 +-removal efficiency of sponge units (> 88%) was significantly higher than that of biofringe units (56−89%). The abundance of amoA gene of ammonia-oxidizing bacteria increased significantly over 56 days and was significantly higher in sponge units than in biofringe units, resulting in higher NH 4 +-removal in sponge units than that in biofringe units. This study demonstrated that dropping nitrification units can be used effectively for NH 4 +-removal from groundwater having a neutral to alkaline pH.

Water, May 7, 2020

Constructed wetlands (CWs) are an effective technology to remove organic compounds and nitrogen (... more Constructed wetlands (CWs) are an effective technology to remove organic compounds and nitrogen (N) from wastewaters and contaminated environmental waters. However, the feasibility of CWs for ammonium-N (NH 4 +-N)-contaminated groundwater treatment is unclear. In this study, zeolite-based laboratory-scale CW was operated as a tidal flow CW with a cycle consisting of 21-h flooded and 3-h rest, and used to treat NH 4 +-N (30 mg L −1) contaminated groundwater. In addition to NH 4 +-N, nitrite (NO 2 −-N) and nitrate (NO 3 −-N) were also not detected in the effluents from the tidal flow CW. The N removal constant remained high for a longer period of time compared to the continuous flow CW. The higher and more sustainable N removal of the tidal flow CW was due to the in-situ biological regeneration of zeolite NH 4 +-N adsorption capacity. Vegetation of common reeds in tidal flow zeolite-based CW enhanced nitrification and heterotrophic denitrification activities, and increased the functional genes of nitrification (AOB-amoA and nxrA) and denitrification (narG, nirK, nirS, and nosZ) by 2-3 orders of magnitude, compared to CW without vegetation. The results suggest that the combination of zeolite substrate, tidal flow, and vegetation is key for the highly efficient and sustainable N removal from NH 4 +-N contaminated groundwater.

Water Science & Technology: Water Supply, Aug 17, 2021

A novel dropping nitrification-cotton-based denitrification reactor was developed for total nitro... more A novel dropping nitrification-cotton-based denitrification reactor was developed for total nitrogen (N) removal from ammonium (NH 4 þ)-contaminated groundwater. The nitrogen removal ability of the reactor was evaluated for 91 days. A 1 m-long dropping nitrification unit was fed with synthetic groundwater containing 30 mg-NH 4 þ-N/L at a flow rate of 2.16 L/d. The outlet of the dropping nitrification unit was connected to the cotton-based denitrification unit. The NH 4 þ present in the groundwater was completely oxidized (.90% nitrification efficiency) by nitrifying bacteria to nitrite (NO 2-) and nitrate (NO 3-) in the dropping nitrification unit. Subsequently, the generated NO 2 and NO 3 were denitrified (96%-98% denitrification efficiency) by denitrifying bacteria in the cotton-based denitrification unit under anoxic conditions. Organic carbons released from the cotton presumably acted as electron donors for heterotrophic denitrification. Nitrifying and denitrifying bacteria were colonized in higher abundance in the dropping nitrification and cotton-based denitrification units, respectively. The total N removal rate and efficiency of the dropping nitrification-cotton-based denitrification reactor for 91 days were 58.1-66.9 mg-N/d and 96%-98%, respectively. Therefore, the dropping nitrification-cotton-based denitrification reactor will be an efficient, sustainable, and promising option for total N removal from NH 4 þ-contaminated groundwater.

Journal of Water and Environment Technology

Tidal flow constructed wetlands (TFCWs) have been proposed as a new type of CW for enhanced waste... more Tidal flow constructed wetlands (TFCWs) have been proposed as a new type of CW for enhanced wastewater treatment. However, the characterization of TFCWs in the removal of organic carbon and nitrogen remains unclear. This study investigated the efficiencies and characteristics of lab-scale TFCWs in removing organic carbon and nitrogen from sewage; in particular, the dynamics of dissolved total organic carbon (DOC), nitrogen, and dissolved oxygen (DO) were observed. Pumice-and zeolite-TFCWs were prepared, which treated sewage at 21 h fill and 3 h rest cycles. Sewage was rapidly oxidized in these TFCWs after inflow. The experimental results showed that DOC was efficiently decreased by aerobic biodegradation with DO consumption. Additionally, NH 4 +-N was oxidized to NO 3 −-N by nitrification, the DO content decreased, and NO 3 −-N was removed by denitrification in the TFCWs. The processes of aerobic-anaerobic switching, organic carbon biodegradation, and nitrification-denitrification were observed in the TFCWs. During 128-days of operation, the pumiceand zeolite-TFCWs exhibited the DOC removal capacities of 4.2 and 4.3 g-DOC/m 2 /d, respectively, and total dissolved inorganic nitrogen removal capacities of 3.1 and 5.1 g-N/m 2 /d, respectively. These results revealed the higher organic carbon and nitrogen removal capacities and mechanisms of pumice-and zeolite-TFCWs treating sewage.

Tropical Aquatic and Soil Pollution, Oct 25, 2021

Heavy metal pollution in water resources has become a serious and hazardous environmental problem... more Heavy metal pollution in water resources has become a serious and hazardous environmental problem all over the world because of its non-biodegradability, emanating from multiple sources, easy accumulation, and biological toxicity. This research was carried out to study the level and distribution of heavy metals at different sampling locations (upstream, midstream, and downstream), at different depths (0.5 m and 1.5 m from surface water level), and during low tide and high tide conditions in the Miri River of Miri City in Malaysia. The river water samples were collected and analyzed for Ca, Mg, Cu, Fe, Mn, Ni, Pb, and Zn by flame atomic absorption spectrophotometer. The concentration of Ca was found to be the highest in the Miri River, followed by Mg and Fe, and with traces of Cu, Mn, Ni, Pb, and Zn. An increase in the concentration of heavy metals, such as Cu, Mg, and Ni, was observed while flowing from upstream to downstream of the Miri River. Concentrations of heavy metals, such as Ca, Mg, Cu, and Zn, were clearly lower at 1.5 m depth than at 0.5 m depth. High tides in the river decrease the concentration of heavy metals, such as Ca, Cu, Mn, and Ni, compared to low tides. From this research, it gets clear that using the Miri River water for domestic and recreational purposes, washing, and fishing is detrimental to human health and the environment.

Nepal Journal of Civil Engineering, 2021

With the rapid urbanization, the production of wastewater is increasing day by day. Direct discha... more With the rapid urbanization, the production of wastewater is increasing day by day. Direct discharge of wastewater in the water bodies/land causes environmental pollutions. Hence, treatment of the wastewater is must, prior to the disposal. Treatment of wastewater through constructed wetlands (CWs) require low cost, less energy consumption, easy construction, and simple operation/maintenance. So, CWs can be the better option for the developing countries such as Nepal. Main objective of the study was to determine the pollutant/nutrient removal abilities of total nitrogen (N), total phosphorous (P), potassium (K+), and biochemical oxygen demand (BOD) in the horizontal subsurface flow (HSSF) CW. The study was carried out in the HSSF CW having gravel as substrate material and common reed (narkat, phragmites karka) as macrophyte. The CW treated domestic wastewater at an average flow rate of 8.64 m3.d−1. The first order removal rate constants were 0.015 m−1 (0.200 d−1) for total N, 0.035 m...

Water Science and Technology

The partial denitrification and anammox (PDA) process has received attention for its ability to o... more The partial denitrification and anammox (PDA) process has received attention for its ability to optimize treatment of wastewater containing a low -N concentration. This study investigated the suitable operational conditions for -N accumulation by hydrogenotrophic denitrification (HD) in operation of a laboratory-scale moving bed biofilm reactor, for future application in the PDA process. -N accumulation was achieved by minimizing the H2 flow rate under optimized conditions (i.e., 15 mL/min H2 flow rate, 40 mg-N/L influent -N, 7.0 h hydraulic retention time, and 2 L working volume). Hydrogenophaga comprised 39.2% of the bacterial abundance after -N accumulated, indicating its contribution to the -N accumulation. In addition, an intermittent H2 supply maintained the -N accumulation rate (NAR) and maximized the nitrite accumulation efficiency (NAE). A H2 supply ratio of 0.7 (i.e., ON: 7 min, OFF: 3 min) was optimal, which induced increases in NAR, NAE, and the -N removal efficiency tha...

Journal of Water and Environment Technology, 2021

Ammonium (NH 4 +) contamination makes groundwater undrinkable. The dropping nitrification unit, a... more Ammonium (NH 4 +) contamination makes groundwater undrinkable. The dropping nitrification unit, a simple and low-cost biological unit, has been found to be effective for NH 4 +-removal from contaminated groundwater at a near-neutral pH. However, the pH of groundwater varies widely and is highly alkaline (pH 8.7−10) in some areas of the world, which could negatively affect the biological nitrification process. The objectives of this study were to investigate the NH 4 +-removal from alkaline groundwater using dropping nitrification units with sponge or biofringe material, compare their removal efficiencies, and characterize the effect of alkaline groundwater on the growth and activity of nitrifying bacteria. Synthetic alkaline groundwater (50 mg-NH 4 +-N L −1 ; pH 9.4 ± 0.1) was dropped from the top of 1-m long hanging units at 3 mL min −1 for 56 days. The NH 4 +-removal efficiency of sponge units (> 88%) was significantly higher than that of biofringe units (56−89%). The abundance of amoA gene of ammonia-oxidizing bacteria increased significantly over 56 days and was significantly higher in sponge units than in biofringe units, resulting in higher NH 4 +-removal in sponge units than that in biofringe units. This study demonstrated that dropping nitrification units can be used effectively for NH 4 +-removal from groundwater having a neutral to alkaline pH.

Industrial and Domestic Waste Management

The elevation of waste generation subsequent to population growth has become a severe environment... more The elevation of waste generation subsequent to population growth has become a severe environmental topic in Malaysia. Since most of the waste is being dumped into a landfill, the open dumpsite, or unsanitary landfills which are not constructed with proper engineering plan, severe impacts on the environment result. The energy demand in Malaysia increased with the growing population, but reliance on fossil fuels to generate electricity has created another greenhouse gas contributor. Alternatively, waste-to-energy technology solves the problem of increasing waste by converting the waste to a renewable energy source. Malaysia has moved towards landfill gas recovery system and incineration for waste energy recovery. The recovery system and refuse-derived fuel plant achieved expectation; however, the incineration plants have failed due to the opposition of the public, lack of funding and technician expertise, and other technical issues. The solid waste management practices lacking separa...

Water, 2021

High nitrate-nitrogen (NO3−–N) content is a typical feature of groundwater, which is the primary ... more High nitrate-nitrogen (NO3−–N) content is a typical feature of groundwater, which is the primary water source in the Kathmandu Valley, Nepal. Considering the Kathmandu Valley’s current problem of water scarcity, a user-friendly system for removing NO3−–N from groundwater is promptly desired. In this study, a simplified hydrogenotrophic denitrification (HD) reactor was developed for the Kathmandu Valley, and its effectiveness was evaluated by its ability to treat raw groundwater. The reactor operated for 157 days and showed stability and robustness. It had an average nitrogen removal efficiency of 80.9 ± 16.1%, and its nitrogen loading rate and nitrogen removal rate varied from 23.8 to 92.3 g–N/(m3∙d) and from 18.3 to 73.7 g–N/(m3∙d), respectively. Compared to previous HD reactors, this simplified HD reactor is a more user-friendly option for the Kathmandu Valley, as most of the materials used for the reactor were locally available and require less maintenance. The reactor is recomme...

Tropical Aquatic and Soil Pollution

Heavy metal pollution in water resources has become a serious and hazardous environmental problem... more Heavy metal pollution in water resources has become a serious and hazardous environmental problem all over the world because of its non-biodegradability, emanating from multiple sources, easy accumulation, and biological toxicity. This research was carried out to study the level and distribution of heavy metals at different sampling locations (upstream, midstream, and downstream), at different depths (0.5 m and 1.5 m from surface water level), and during low tide and high tide conditions in the Miri River of Miri City in Malaysia. The river water samples were collected and analyzed for Ca, Mg, Cu, Fe, Mn, Ni, Pb, and Zn by flame atomic absorption spectrophotometer. The concentration of Ca was found to be the highest in the Miri River, followed by Mg and Fe, and with traces of Cu, Mn, Ni, Pb, and Zn. An increase in the concentration of heavy metals, such as Cu, Mg, and Ni, was observed while flowing from upstream to downstream of the Miri River. Concentrations of heavy metals, such a...

Water

Constructed wetlands (CWs) are an effective technology to remove organic compounds and nitrogen (... more Constructed wetlands (CWs) are an effective technology to remove organic compounds and nitrogen (N) from wastewaters and contaminated environmental waters. However, the feasibility of CWs for ammonium-N (NH4+-N)-contaminated groundwater treatment is unclear. In this study, zeolite-based laboratory-scale CW was operated as a tidal flow CW with a cycle consisting of 21-h flooded and 3-h rest, and used to treat NH4+-N (30 mg L−1) contaminated groundwater. In addition to NH4+-N, nitrite (NO2−-N) and nitrate (NO3−-N) were also not detected in the effluents from the tidal flow CW. The N removal constant remained high for a longer period of time compared to the continuous flow CW. The higher and more sustainable N removal of the tidal flow CW was due to the in-situ biological regeneration of zeolite NH4+-N adsorption capacity. Vegetation of common reeds in tidal flow zeolite-based CW enhanced nitrification and heterotrophic denitrification activities, and increased the functional genes of ...

Water

A dropping nitrification reactor was proposed as a low-cost and energy-saving option for the remo... more A dropping nitrification reactor was proposed as a low-cost and energy-saving option for the removal of NH4+-N from contaminated groundwater. The objectives of this study were to investigate NH4+-N removal performance and the nitrogen removal pathway and to characterize the microbial communities in the reactor. Polyolefin sponge cubes (10 mm × 10 mm × 10 mm) were connected diagonally in a nylon thread to produce 1 m long dropping nitrification units. Synthetic groundwater containing 50 mg L−1 NH4+-N was added from the top of the hanging units at a flow rate of 4.32 L day−1 for 56 days. Nitrogen-oxidizing microorganisms in the reactor removed 50.8–68.7% of the NH4+-N in the groundwater, which was aerated with atmospheric oxygen as it flowed downwards through the sponge units. Nitrogen transformation and the functional bacteria contributing to it were stratified in the sponge units. Nitrosomonadales-like AOB predominated and transformed NH4+-N to NO2−-N in the upper part of the reacto...