Indonesia is host to a long history of gold mining and is responsible for a significant contribution to world gold production. This is true not only with regard to large gold mining companies but also to small-scale mining groups comprised of people and enterprises that participate in the gold industry of Indonesia. More than two thousand gold mining locations exist in present day Indonesia. Artisanal and small-scale gold mining (ASGM) sites are spread out across thirty provinces in Indonesia, and have provided work opportunities and income for more than two million people. However, the majority of ASGM activities use rudimentary technologies that have serious impacts upon the environment, public health, and miners’ safety, which in turn generate socio-economic impacts for people residing around the mine sites. Moreover, many ASGMs are not licensed and operate illegally, meaning that they are immune to governmental regulation, and do not provide income to the regions and states via taxes. The possibility for more prudent management of ASGM operations could become a reality with the involvement and cooperation of all relevant parties, especially communities, local government, police, and NGOs.
Wastewater treatment by constructed wetland is an appropriate technology for tropical developing countries like Indonesia because it is inexpensive, easily maintained, and has environmentally friendly and sustainable characteristics. The aim of the research is to examine the capability of constructed wetlands for treating laboratory wastewater at our Center, to investigate the suitable flow for treatment, namely vertical subsurface or horizontal surface flow, and to study the effect of the seasons. The constructed wetland is composed of three chambered unplanted sedimentation tanks followed by the first and second beds, containing gravel and sand, planted with Typha sp.; the third bed planted with floating plant Lemna sp.; and a clarifier with two chambers. The results showed that the subsurface flow in the dry season removed 95% organic carbon (COD) and total phosphorus (T-P) respectively, and 82% total nitrogen (T-N). In the transition period from the dry season to the rainy season, COD removal efficiency decreased to 73%, T-N increased to 89%, and T-P was almost the same as that in the dry season. In the rainy season COD and T-N removal efficiencies increased again to 95% respectively, while T-P remained unchanged. In the dry season, COD and T-P concentrations in the surface flow showed that the removal efficiencies were a bit lower than those in the subsurface flow. Moreover, T-N removal efficiency was only half as much as that in the subsurface flow. However, in the transition period, COD removal efficiency decreased to 29%, while T-N increased to 74% and T-P was still constant, around 93%. In the rainy season, COD and T-N removal efficiencies increased again to almost 95%. On the other hand, T-P decreased to 76%. The results show that the constructed wetland is capable of treating the laboratory wastewater. The subsurface flow is more suitable for treatment than the surface flow, and the seasonal changes have effects on the removal efficiency.
Denitrification of nitrite-nitrogen carried out experimentally in an anoxic two-phase fluidized bed bioreactor is described, and the characteristics of the biological treatment were also theoretically studied. Methanol was used as the carbon source, and nitrite-degrading bacteria immobilized on CB particles were employed. A method for evaluating the characteristics of the biological treatment is proposed. Within the range of the experiment, the results show that denitrification of nitrite-nitrogen could be approximated by Monod-type reaction kinetics, characteristic values for the biological treatment of Ku = 5.0 kg-N·kg−1-VS·d−1 and Ku/Km = 23.8 m3·kg−1-VS·d−1 being obtained. There was good correlation between the experimental results and the calculated curves. A maximum volumetric denitrification rate for nitrite of 18.7 kg-N·m−3·d−1 was achieved, this high value demonstrating the high efficiency of an anoxic two-phase fluidized bed bioreactor to denitrify nitrite-nitrogen.
luidized bed bioreactors have attracted much attention for several years because they are more efficient in removing pollutants such F as phenol from industrial wastewater than conventional activated sludge. So far, these reactors have been successfully used for the treatment of several kinds of wastewater such as coke oven waste (Hirata et al., 1991 a), kitchen wastewater (Hirata et al., 1991 b), nitrite-nitrogen containing wastewater (Hirata and Meutia, 1996) and washing-drum wastewater in a pilot study (Hirata et al., 1992). However, since the reactor operation is quite difficult particularly with a plug-flow type fluidized bed (Hirata and Noguchi, 1994), the characteristics of simultaneous utilization of oxygen and substrate in this reactor should be elucidated.As described previously (Hirata et al., 1990(Hirata et al., , 1998, the biodegradation of a high concentration of phenol (above 0.04 k g~n -~) in a three-phase fluidized bed bioreactor led to the conclusion that the reaction rate was considered to follow zero-order reaction kinetics with respect to phenol. Tang and Fan (1987) found that the phenol removal rate was independent of the dissolved oxygen concentration at a condition of sufficiently high oxygen concentration. On the other hand, according to Worden and Donalson (1 987), when the dissolved oxygen concentration increased, the reaction rate would increase. In the case of low dissolved oxygen concentration (aerated with air), the reaction rate was found to be approximated as first-order with respect to oxygen (Hirata et al., 1990).In this study, the effects of superficial gas velocity (UJ, oxygen concentration in the gas phase, and specific biofilm interfacial area (a,) on the volumetric phenol removal rate (R,lV), were evaluated both theoretically and experimentally. A semi-theoretical equation was developed for predicting the volumetric removal rate and used to explain the overall removal rate of phenol. TheoryThe semi-theoretical equation was developed using the basic equations of a three-phase fluidized bed bioreactor model as described in previous paper (Hirata et al., 1990). In this model, the flow characteristic in the tubular-type reactor is assumed to be a plug flow. Judging from the size ratio of the height to the diameter, 64, it is reasonable to propose the plug flow assumption, which has been supported by many old reports on the basis of "complete mixing vessel row model" (Aris and Amundson, 1957). When oxygen concentration was low and phenol concentration was high, the reaction rate was considered to follow firstorder reaction kinetics with respect to oxygen, and zero-order kinetics 'Author to whom correspondence may be addressed. E-mail address: hirata@mn. waseda.ac.jpThe effects of oxygen supply conditions and specific biofilm interfacial area on the phenol removal rate in a three-phase fluidized bed bioreactor were evaluated. The experimental data were well-explained by the semi-theoretical equation based on the assumption that the reaction rate follows first-order reaction ki...
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