Material and monetary flows of construction and demolition waste and assessment on physical and environmental properties of illegally dumped construction and demolition waste in Hanoi.

The main aim of this study is to investigate the material and monetary flows of CDW management and to characterize the distribution of illegally dumped CDW in Hanoi. Construction and demolition waste management has become a source of much concern to the urban authorities and citizens of big cities in Vietnam. It is estimated that 3000 t of CDW were generated per day from construction and demolition activities in Hanoi, but only 45% of the CDW was received at official landfills, while 55% of the CDW was disposed of elsewhere. The consequences of improper waste management are potentially alarming. The study conducted interviews to identify the material and cash flow associated with licensed and unlicensed contractors in CDW classification, transportation, treatment, and disposal, to characterize the distribution of illegally dumped CDW in two districts in Hanoi (urban and suburban districts), and to assess the composition of dumped CDW and environmental assessment of illegally dumped CDW by chemical analyses such as leaching and content tests. The study concluded that illegal dumping was performed mostly by unlicensed private companies. The illegally dumped CDW was mostly composed of mixed materials such as concrete, bricks, stones, and some hazardous materials such as asbestos and gypsum were found. The environmental concern of illegally dumped CDW was mostly dust, blockage of water ways, and inundation of increased suspended solids, whereas the heavy metal leaching concentration of all samples was below the environmental standards in Vietnam.

Effect of Hydraulic retention time on performance of anaerobic membrane bioreactor treating slaughterhouse wastewater.

Slaughterhouse wastewater is a major environmental concern in many Vietnamese cities due to its high organic content and unpleasant odor. This study aimed to evaluate performance of a submerged flat sheet Anaerobic membrane bioreactor (AnMBR) system at different hydraulic retention time (HRT, 8-48 h) treating wastewater from a slaughterhouse in Hanoi City (Vietnam) at ambient temperature. The wastewater characteristics were as follows: chemical oxygen demand (COD) of 910 ± 171 mg/L; suspended solids (SS) of 273 ± 139 mg/L; and total nitrogen (T-N) of 115 ± 31 mg/L. The AnMBR system achieved high removal efficiencies for SS (99%) and COD (>90%) at an optimum HRT of 24 h. The biomethane yield reached 0.29 NL CH4/g CODinf. Importantly, the system maintained stable operation without flux decay and membrane fouling. HRT longer than 24 h could offer the better effluent quality without an increase in transmembrane pressure (TMP); however, it led to a lower methane production rate. Shorter HRT of 8-12 h caused a high TMP over -10 kPa, posing a risk for membrane fouling and biomass loss during cleaning, thus resulting in a low methane production. Our results suggest that AnMBR can be a reliable technology for wastewater treatment, reuse and energy recover from slaughterhouse wastewater in Vietnam and other similar climate countries.

Effect of carbohydrates on protein hydrolysis in anaerobic digestion.

This study aimed to assess the effect of carbohydrates on protein hydrolysis and potential implications for the design of anaerobic reactors for treatment of protein-rich wastewaters. Batch experiments were carried out with dissolved starch (Sta) and gelatine (Gel) at different chemical oxygen demand (COD) ratios ranging from 0 to 5.5 under methanogenic conditions for methane production and up to 3.8 under non-methanogenic conditions for volatile fatty acids (VFA), both at 35 °C. The Sta/Gel did not have a direct effect on the gelatine hydrolysis rate constants under methanogenic (0.51 ± 0.05 L g VSS-1 day-1) and non-methanogenic conditions (0.48 ± 0.05 L g VSS-1 day-1). However, under non-methanogenic conditions, gelatine hydrolysis was inhibited by 64% when a spectrum of VFA was added at a VFA/Gel (COD) ratio of 5.9. This was not caused by the ionic strength exerted by VFA but by the VFA itself. These results imply that methanogenesis dictates the reactor design for methane production but hydrolysis does for VFA production from wastewater proteins.

Steel slag quality control for road construction aggregates and its environmental impact: case study of Vietnamese steel industry-leaching of heavy metals from steel-making slag.

Steel slag is an industrial by product of steel manufacturing processes and has been widely utilized within civil and construction materials for road materials and environmental remediation in countries like Japan, USA, and European Union nations. However, the current utilization of steel slag in Vietnam is very low mainly because of lack of quality control of slag treatment and chances for reuse of treated steel slag. This paper presents the up to date steel slag production status in Vietnam through the extensive survey and sampling at seven large steel factories. The paper also highlights the environmental and quality control issues of these steel slags to use as road construction aggregates by assessing the heavy metals concentration in the leachate. The basic oxygen furnace (BOF) and electric arc furnace (EAF) slag samples were collected to evaluate leaching properties of metals leached from the slags. The two standardized batch leaching tests of steel slag roadbed material in Japan (JIS K 0058-1) and toxicity characteristics leaching procedure (TCLP-EPA method 1311) were performed to the evaluated the hazardous metals. The results of the leaching test show that almost all of the concentration of the metals in the leached solution does not exceed the National Standard for Industrial Wastewater Discharge (QCVN 40-2011). The pH and parameters such as total chromium, nickel, copper, lead, arsenic, and manganese differ from the two test methods. The acidic conditions employed in the EPA 1311 were not representative of condition excepted during slag reuse in road constructions because in the operation condition of the road, acidic liquid is absent. The leaching test results confirmed that JIS test which uses deionized water with gentle mixing prevents the slag sample from size degradation is suitable for the environmental assessment of steel slag use for roadbed material. This research suggests that the adjustment of pH value prior to disposal or reuse as base materials and official guideline should be promulgate by the authorities to ensure the leachate meet the surface water quality standard.