On-site Domestic Wastewater Treatment Research Articles

The use of vertical flow constructed wetlands for on-site treatment of domestic wastewater: New Danish guidelines

Official guidelines for the on-site treatment of domestic sewage have recently been published by the Danish Ministry of Environment as a consequence of new treatment requirements for single houses and dwellings in rural areas. This paper summarises the guidelines for vertical constructed wetland systems (planted filter beds) that will fulfil demands of 95% removal of BOD and 90% nitrification. The system can be extended with chemical precipitation of phosphorus with aluminium polychloride in the sedimentation tank to meet requirements of 90% phosphorus removal. The necessary surface area of the filter bed is 3.2 m 2/person equivalent and the effective filter depth is 1.0 m. The filter medium must be filtersand with a d 10 between 0.25 and 1.2 mm, a d 60 between 1 and 4 mm, and a uniformity coefficient ( U = d 60/ d 10) less than 3.5. The sewage is, after sedimentation, pulse-loaded onto the surface of the bed using pumping and a network of distribution pipes. The drainage layer in the bottom of the bed is passively aerated through vertical pipes extending into the atmosphere in order to improve oxygen transfer to the bed medium. Half of the nitrified effluent from the filter is recirculated to the first chamber of the sedimentation tank or to the pumping well in order to enhance denitrification and to stabilise the treatment performance of the system. A phosphorus removal system is installed in the sedimentation tank using a small dosing pump. The mixing of chemicals is obtained by a simple airlift pump, which also circulates water in the sedimentation tank. The vertical flow constructed wetland system is an attractive alternative to the common practice of soil infiltration and provides efficient treatment of sewage for discharge into the aquatic environment.

Requirements and test methods for on site domestic wastewater treatment plants: the European standard (prEN 12566-3) compared to other international standards

To ensure that domestic wastewater treatment plants run in an efficient and reliable way, certifications already exist while others will be implemented soon. To date, we have listed eight standards: four from European countries (Germany, Great Britain, The Netherlands and Norway), one project from the European Union, two from North America (USA and Quebec) and one from Australia and New Zealand together. The European procedure includes verification of structure stability, water tightness and treatment capacity at test centre (38 weeks). The American Standard sets minimal standards for materials, dimensioning, building and performances of the plants. It also highlights the information and minimum service that should be provided by the manufacturer and distributors. The review process relating to treatment performances shares major similarities with the EU project since both documents were elaborated almost simultaneously. Australia and New Zealand have adopted a series entitled On-site Domestic Wastewater Treatment Units made up of three parts. The third one integrates construction requirements and describes quite an interesting procedure to efficiently test the small plant: after approximately 13 weeks of testing (half the total duration), the aeration chamber (provided it exists) is filled with sludge from septic tanks to simulate its operation after several years. Overview of the treatment efficiency test procedures of the three main standards is given.

Enhancement of oxygen transfer and nitrogen removal in a membrane separation bioreactor for domestic wastewater treatment

Biological nitrogen removal in a membrane separation bioreactor developed for on-site domestic wastewater treatment was investigated. The bioreactor employed hollow fiber membrane modules for solid-liquid separation so that the biomass could be completely retained within the system. Intermittent aeration was supplied with 90 minutes on and off cycle to achieve nitrification and denitrification reaction for nitrogen removal. High COD and nitrogen removal of more than 90% were achieved under a moderate temperature of 25 degrees C. As the temperature was stepwise decreased from 25 to 5 degrees C, COD removal in the system could be constantly maintained while nitrogen removal was deteriorated. Nevertheless, increasing aeration supply could enhance nitrification at low temperature with benefit from complete retention of nitrifying bacteria within the system by membrane separation. At low operating temperature range of 5 degrees C, nitrogen removal could be recovered to more than 85%. A mathematical model considering diffusion resistance of limiting substrate into the bio-particle is applied to describe nitrogen removal in a membrane separation bioreactor. The simulation suggested that limitation of the oxygen supply was the major cause of inhibition of nitrification during temperature decrease. Nevertheless, increasing aeration could promote oxygen diffusion into the bio-particle. Sufficient oxygen was supplied to the nitrifying bacteria and the nitrification could proceed. In the membrane separation bioreactor, biomass concentration under low temperature operation was allowed to increase by 2-3 times of that of moderate temperature to compensate for the loss of bacterial activities so that the temperature effect was masked.

Evaluation of an Economical Alternative Onsite Domestic Wastewater Treatment System to Remove Soluble and Particulate Organic Oxygen Demand

Evaluation of an Economical Alternative Onsite Domestic Wastewater Treatment System to Remove Soluble and Particulate Organic Oxygen Demand

Development of Phosphorus Removal Process of On-site Domestic Wastewater Treatment Systems Using Dripping Method of Thick Iron Solution.

An advanced technique of dripping the thick iron solution was developed and applied to on-site domestic wastewater treatment systems. The thick iron solution was obtained by heating and melting FeCl3⋅6H2O crystals.By using the new technique, the T-P concentration of the treated water decreased to less than 1mg·l-1 when the thick iron solution was added at an Fe/P molar ratio of 1.75. The addition of thick iron solution did not affect the removal of BOD, COD, SS and T-N.The T-P concentration of the treated water increased when coagulated sludge containing ferric phosphate was in contact with the anaerobic sludge in the tank for along time. This problem could be solved by improving the process to prevent such contact. It was also shown that the addition of thick iron solution increased the volume of sludge by about 30%.

On-site domestic wastewater treatment by reed bed in the moist subtropics

This paper summarises the results of studies on four subsurface flow wetlands (reed beds) located in the moist sub-tropical north eastern corner of the Australian state of New South Wales. The reed beds, which are subjected to a variety of effluent types, all have a gravel substrate planted with Phragmites australis. All four units were found to maintain satisfactory treatment performance year round. Mean removal efficiencies ranged from 56% to 90% (SS), 70% to 93% (BOD), 38% to 66% (TN), 87% to 99.8% (Faecal coliforms), and 42% to 70% (TP--with one seasonal result of 0% for the eight year old unit) for the four reed beds. After eight years in operation the oldest reed bed was showing signs of phosphorus saturation with outlet TP concentrations exceeding inlet concentrations on some occasions. The youngest reed bed studied appeared to be operating efficiently after five months. A summer water balance on one of the reed beds revealed an average crop factor of 1.6 and a moisture loss to atmosphere of 40% of influent flow. Treatment performance (particularly for TN and SS) was found to be negatively correlated with rainfall during one study. The paper discusses the implications of the above results for on-site system designers and regulators and identifies areas for further investigation.

Uptake of 15N by Macrophytes in Subsurface-Flow Wetlands Treating Domestic Wastewater

Constructed subsurface-flow wetlands are becoming more common for on-site treatment of domestic wastewater to provide secondary quality effluent. Macrophytes are generally added to wetlands to increase treatment efficiency but their role in reducing N content is controversial. Our investigation utilized two subsurface-flow wetlands to determine the efficiency of different macrophytes in uptake of 15N labeled ammonium sulfate. Macrophytes in Wetland 1 recovered 35 % of the added N in their shoots but only 5 % of the added N was recovered in the shoots and roots in Wetland 2. A major difference for the two wetlands was N and hydraulic loadings. Wetland 1 received 7.5 Kg N ha-1d-1 and Wetland 2 received 16.9 Kg N ha-1d-1. Retention time for Wetland 1 based on pore volumes was 2.9 d and for Wetland 2 it was 1.2 d. The retardation factor for NH4+ was approximately 2.5 for both wetlands and the breakthrough curves indicated lack of plug flow. The importance of macrophytes in taking up NH4 appeared to dependent on N and hydraulic loadings.

New technologies for on-site domestic and agricultural wastewater treatment

Recently publicized problems of water quality in rural parts of Canada are again bringing increasing attention to methods of dealing with wastewater in rural environments. This includes wastewater from both domestic (principally single-family homes) and agricultural sources. Previous practices which relied on dispersal with little treatment are increasingly unacceptable not only because of the recognition of the weakness of this approach but also because of the increasing intensification of land use in rural areas. Thus the need for additional and improved technologies for treating wastewater, on site, has increased. Because of this, new technologies have been developed which provide better treatment than previous approaches that also rely on natural processes. Examples of the former include peat, sand, and foam filters for domestic on-site wastewater systems. Engineered wetlands to treat barnyard runoff or rural municipal lagoon effluent is an example of a technology using natural processes. This paper describes some of these new technologies and their potential advantages.Key words: rural, wastewater, septic, manure, farm, on site, technologies.

New technologies for on-site domestic and agricultural wastewater treatment

New technologies for on-site domestic and agricultural wastewater treatment

嫌気槽に鉄材を浸漬する簡易なリン除去

A simplified phosphorus removal method for the small-scale on-site domestic wastewater treatment systems, which have been used for disposal of domestic wastewater, was examined.This method consisted of submerging the iron media in an anaerobic chamber. Phosphorus could be effectively removed even at a low oxygen concentration in the anaerobic chamber.The phosphorus removing effect in the anaerobic environment was examined in different iron media. Iron cations were dissolved from steel wool more than from other media, because of the relatively large surface area.The phosphorus removal method was examined using a continuous experimental apparatus. To obtain 90% phosphorus removal, it was necessary to submerge the iron media of 6.6kg·m-3 or more, and to maintain phosphorus-iron surface area loading to be 0.05g·m-2·d-1 or less.The iron surface was covered gradually with reaction products and captured SS, and the weight of iron increased. After 2 months of submersion of iron media, dissolution of iron cations was hindered, and phosphorus removal decreased markedly. Therefore, periodic back-wash at least every 2 months was considered necessary.Phosphorus removal cost was calculated. This method was considered to be expensive about 30-160%. However, it is possible to reduce the cost further by periodic maintenance.

The use of a zeolite-iron column for residual ammonia and phosphorus removal in the effluent from a membrane process as an on-site small-scale domestic wastewater treatment

Laboratory-scale experiments were performed to investigate the performance of the on-site small-scale combined system of membrane separation bioreactor (MSB) and zeolite-iron (Z-Fe) column. Average nitrogen removal by the membrane separation bioreactor was varied from 83% at an influent nitrogen concentration of 30 mg/l to 50% at 75 mg/l. Residual ammonia nitrogen in the effluent from the membrane separation bioreactor was further polished by a Z-Fe column to an initially non-detectable concentration and finally to 1.2 mg/l. The average phosphorus removal by this column unit was 70%. Improvement by providing aeration to the bottom part of iron bed in the long column improved phosphorus removal efficiency to as much as 92% until water logging occurred inside the column. Moreover, further improvement was achieved by inserting three short columns in series for 116 day of operation. Average effluent phosphorus concentrations of 1.2, 0.39 and 0.16 mg/l were obtained after the 1st, 2nd and 3rd column respectively with an applied influent phosphorus concentration of 5.3 mg/l on average. Furthermore, batch experiments were carried out to investigate the factors, such as pH and temperature, which affect the performance of the Z-Fe column in phosphorus removal.

Biological Nitrogen Removal under Low Temperature in a Membrane Separation Bioreactor

Biological nitrogen removal under low temperature in a membrane separation bioreactor for on-site domestic wastewater treatment was studied. The bioreactor was operated under intermittent aeration of a 180-minute operational cycle to achieve simultaneous nitrification and denitrification for nitrogen removal. During stepwise temperature decrease from 25°C to 5°C at every two weeks duration, nitrogen removal started to deteriorate as temperature dropped to 10°C. It decreased from more than 90% at 25°C to 20% at 5°C as a result of inhibition of nitrification at low temperature. However, increasing oxygen supply, i.e. increasing aeration time in operational cycle, could completely recover nitrification at 10°C. Nitrogen removal could be achieved by introducing non-aeration period after complete nitrification was obtained. Average nitrogen removal was 90 and 85% under 10 and 5°C respectively. The results indicated that sufficient oxygen transfer could be maintained in the membrane separation bioreactor even if the temperature was as low as 5°C. Analysis of respiratory quinone component of sludge suggested the decrease of strict aerobic bacteria percentage in mixed liquor during temperature decrease and increase of their percentage during the recovery of nitrification at 10°C. These changes could be related to the nitrification through the changes of oxygen transfer condition in the system. Insignificant difference of maximum volumetric nitrification rate obtained at 25 and 5°C probably suggests that there was not much difference in oxygen availability for nitrifying bacteria between both the temperatures once high and stable nitrogen removal was achieved.

Anaerobic Treatment of Domestic Wastewater in Small Scale UASB Reactors

A survey was made on the feasibility of on-site anaerobic treatment of domestic wastewater from small scale emissions in The Netherlands. Three 1.2 m3 UASB-reactors (Upflow Anaerobic Sludge Blanket) were tested in different rural locations. The survey made clear that the efficiency of the process is highly dependent on the reactor temperature. Below 12 °C purification was predominantly based on settling, while above 12 °C microbial degradation of organic matter increased. Efficiencies for the removal of total COD and BOD of two of the reactors ranged between 33 and 60%, equalising well performing septic tanks. In one of the reactors the average production of biogas, with a methane content of 78%, was 67 liters per day. Complete transformation of volatile fatty acids (VFA) into biogas was achieved during 3 to 4 months a year at temperatures above 15 °C. In this period, during the second year of operation, the average efficiencies for COD and BOD removal were 60 and 72% respectively, while the maximum gas production reached 300 liters per day. In the latter period the mineralisation rate exceeded the input rate of organic matter, resulting in a decrease of settled material in the reactor. The possibility of high efficiencies during summertime in The Netherlands and the positive results of similar experiments in Indonesia and Latin America lead to the conclusion that anaerobic digestion is a promising process for the (pre-)treatment of domestic waste water in (sub)tropical countries.

High Performance and N & P-Removable On-Site Domestic Waste Water Treatment System by Multi-Soil-Layering Method

Multi-Soil-Layering (MSL) method was applied to make appropriate, but high performance and N & P-removable, on-site domestic waste water treatment system. The MSL soil unit is composed from soil layer mixed with 10∼25% of metal iron and pelletized jute. The MSL units were piled in a brick pattern at 5cm vertical and 10cm horizontal distance, which were surrounded by layers of Zeolite. Air can be supplied through porous pipes installed at adequate depths of the MSL system. The systems were tested using model houses. The waste waters, which were pretreated by septic tank to the level of SS 29-75, BOD 42-116, COD 32-56, T-N 29-86, and T-P 6-11 mg−l−1 respectively, could be treated at the rate of 100-850 1·m−2·d−1 without significant clogging. The mean concentrations of treated waters were SS 15, BOD 8.7, COD 11, T-N 6.8, and T-P 0.86 mg·1−1 respectively. Zeolite layers and brick pattern prevent clogging. Metal iron and jute pellets were effective to remove Phosphate and Nitrate. Intensive aeration assists decomposition of BOD, COD, and SS as well as nitrification, but decreases denitrif ication and phosphate fixation. The degree of purification could be controlled by setting adequate aeration.

Anaerobic and Aerobic Submerged Bio-Filter System for Small Scale On-Site Domestic Sewage Treatment

In order to prevent water pollution and satisfy the demands for flush toilets in regions where a public sewerage system has not been in service, some on-site small scale domestic wastewater treatment processes called GAPPEI JOHKASOU have been developed to treat black water and gray water together in an individual house. Prior to its technical development, the characteristics of wastewater discharged from individual houses should be measured. The possibility of application of anaerobic filter is examined for processing organic wastewater at low concentration like in domestic wastewater, and an anaerobic filteris successfully developed to lengthen the sludge removal interval, since the flow rate of wastewater from individual houses is characterized by a large variation. It is difficult to serve the centralized treatment systems in many regions. Thus, a small GAPPEI JOHKASOU has been developed and propagated for by individual houses in such regions.

エネルギー・アナリシスによる水循環システムの評価

This paper appraised 4 models of water recycle systems in urban area such as wastewater reuse system and rain water usage from the point of view of energy consumption.Input-output analysis was used for the calculation of energy consumption. Not only the direct energy such as electric power and fuel but also the indirect energy used for production of equipments or parts in the water system were taken into consideration.The main results obtained were as follows.(1) The least energy consumption model was unrecycle model.(2) The largest energy consumption model was individual recycle model, but in low-densed areas below 90-150 households/km2 it was advantageous than unrecycle model.(3) The energy consumption of wastewater reuse system was mainly attributed to the distribution system and was about 15% more than that of water works.(4) Recharge of groundwater by infiltration of rain water was better than on-site rain water usage because FRP water tanks consumed a large amount of energy.(5) Works such as water treatment or water distribution consumed about 50% of the maintenance energy in unrecycle model and the rest was considered to be consumed in the business in the works.(6) From the aspects of the energy consumption, johkaso (on-site domestic wastewater treatment system) was advantageous than sewage works in areas below 196 households/km2.