Sewage sludge produced from wastewater treatment is one of the challenges facing many countries in their development process; therefore, the sewage sludge needs treating suitably. Besides, recovering energy from waste to save operating costs in treatment plants is also being considered. The study was conducted by mixing urban sludge samples with substrates (agricultural residues) to create different C/N ratios from 16.6 to 32.5, then evaluating the quantity and quality of methane) the gas generated from the test pieces. This method not only solved the environmental problem but also had benefited from biogas produced from the digestion process. The initial results showed that the quantity of biogas from anaerobic co-digestion of sewage sludge and rice husk (ratio 4:1) are 160ml/g VS. Furthermore, the quality of methane can be up to 60% and near twice as much as mono-digestion. The study results estimate that the potential of recovering electricity from the sludge for the wastewater treatment plant of Binh Hung (Vietnam) is about 0.2 MW/year or higher.

Chemical fertilizers currently poison arable agriculture, so organic fertilizers are now a new trend for soil improvement. This study investigates the appropriate ratio of fertilizer use and materials mixed with sewage sludge in the anaerobic co-digestion treatment method, which will best support agriculture. In the study, bio-organic fertilizer was composted of the co-digestion anaerobic with sewage sludge and agricultural wastes such as rice husk, rice husk charcoal, water hyacinth, cassava peel, and then tested on rice. The specific criteria of fertilizers such as total organic (TOC), total nitrogen (TN), and effective phosphorus (P2O5) and plant growth parameters such as germination rate (%), tillering rate, total weight (g) were evaluated. Initial results show the untreated sludge can be impacted negatively on plant development. The concentration of nutrients in the co-digestion composts was meet the requirements of the Ministry of Agriculture’s standards of organic fertilizer. These bio-fertilizers will play an important role in soil productivity and sustainability. Hence, the widespread use of organic fertilizers from waste to partially replace chemical fertilizers will open up opportunities to reduce farming costs for farmers and develop agriculture sustainably.

Reuse of biosolids aiming to take advantage of its nutrients and micronutrients for arable crops is an economical approach, in which wastes are considered potential resources and bring a variety of benefits. However, heavy metal residuals in sewage sludge have been gaining attention due to accumulation risk and adverse effects on the environment. This study experimented with sludges from Binh Hung municipal wastewater treatment plants treated by anaerobic co-digestion process on corn seed LVN10 to assess corn growth and heavy metals accumulation contents in various components of the corn and the soil. Consequently, within 90 days of using biosolids as treatments 1% and 3%, i.e., the corresponding amount of biosolids over the soil weight, there was no inhibition but growth stimulation for corn growth surveyed. Accumulations of Cu, Cd, Pb, Zn, Ni in roots, stalk, leaves, and mature corn and cultivated soil complied with the national regulations. The effectiveness of biosolids application for corn production in this study will benefit the depreciation of sludge production from municipal wastewater treatment plants and other applications for agricultural plants in the future.