Struvite production from anaerobic digestate of piggery wastewater using ferronickel slag as a magnesium source.

This study aimed to fully recover ammonia contained at a high concentration in anaerobic digestate of piggery wastewater (ADPW) by forming struvite. As magnesium and phosphorus sources, ferronickel slag (FNS) and K2HPO4 were used, respectively. By leaching 200 g L-1 of FNS with 3.0 M H2SO4, 10,309 mg L-1 of magnesium ions were extracted, and this acid-leachate of FNS (FNSL) also contained 5965 mg L-1 of total iron. In order to simultaneously remove both high concentrations of organic matters in ADPW and iron in FNSL which were known to hinder struvite formation, the mixture of ADPW and FNSL was added with H2O2 at the H2O2/Fe molar ratio of 0.75 and pH 4.0. After Fenton reaction, removal efficiencies of COD and total iron reached 77.36% and 99.89%, respectively. Then COD and an iron-reduced mixture of ADPW and FNSL were added with K2HPO4 satisfying Mg:N:P molar ratio of 1.2:1:1.15 at pH 9.5 to produce struvite for 1 h. From 1 L of ADPW (2.21 g NH3-N), 0.65 L of FNSL (4.65 g Mg2+), and 5.63 g of PO4 3-P, 46.7 g of precipitates were obtained. Overall removal efficiencies of magnesium, NH3-N, and phosphorus were 98.59%, 94.25%, and 99.97%, respectively. Obtained precipitates were analysed by using XRD, XRF, SEM-EDX and found to be struvite with impurities of potassium and metals. Additionally, the economic feasibility of FNS was assessed by estimating chemical costs of various magnesium sources.

Effect of ciprofloxacin dosages on the performance of sponge membrane bioreactor treating hospital wastewater.

This study aimed to evaluate treatment performance and membrane fouling of a lab-scale Sponge-MBR under the added ciprofloxacin (CIP) dosages (20; 50; 100 and 200 µg L-1) treating hospital wastewater. The results showed that Sponge-MBR exhibited effective removal of COD (94-98%) during the operation period despite increment of CIP concentrations from 20 to 200 µg L-1. The applied CIP dosage of 200 µg L-1 caused an inhibition of microorganisms in sponges, i.e. significant reduction of the attached biomass and a decrease in the size of suspended flocs. Moreover, this led to deteriorating the denitrification rate to 3-12% compared to 35% at the other lower CIP dosages. Importantly, Sponge-MBR reinforced the stability of CIP removal at various added CIP dosages (permeate of below 13 µg L-1). Additionally, the fouling rate at CIP dosage of 200 µg L-1 was 30.6 times lower compared to the control condition (no added CIP dosage).

Spent coffee ground as a new bulking agent for accelerated biodrying of dewatered sludge.

The feasibility of using spent coffee ground (SCG) as a new bulking agent for biodrying of dewatered sludge (DS) was investigated in comparison with two other frequently-used bulking agents, air-dried sludge (AS) and sawdust (SD). Results showed that the moisture contents (MC) of 16-day DS biodrying with AS (Trial A), SCG (Trial B) and SD (Trial C) decreased from 70.14 wt%, 68.25 wt% and 71.63 wt% to 59.12 wt%, 41.35 wt% and 57.69 wt%, respectively. In case of Trial B, the MC rapidly decreased to 46.16 wt% with the highest water removal (70.87%) within 8 days because of the longest high-temperature period (5.8 days). Further studies indicated that the abundant biodegradable volatile solids (BVS) and high dissolved organic matter (DOM) contents in SCG were the main driving forces for water removal. According to pyrosequencing data, Firmicutes, most of which were recognized as thermophiles, was rapidly enriched on Day 8 and became the dominant phylum in Trial B. Four thermophilic genera, Bacillus, Ureibacillus, Geobacillus and Thermobifida, which can produce thermostable hydrolytic extracellular enzymes, were the most abundant in Trial B, indicating that these thermophilic bacteria evolved during the long high-temperature period enhanced the biodegradation of BVS in SCG. The 8-day biodried product of Trial B was demonstrated to be an excellent solid fuel with low heating value (LHV) of 9284 kJ kg-1, which was 2.1 and 1.8 times those of biodried products with AS and SD, respectively. Thus SCG was found to be an excellent bulking agent accelerating DS biodrying and producing a solid fuel with a high calorific value.

Recovery of ammonia through struvite production using anaerobic digestate of piggery wastewater and leachate of sewage sludge ash.

Anaerobic digestate of piggery wastewater (ADPW) contains high concentrations of ammonia and phosphorus with unbalanced molar ratio. Thus, ammonia remains at a high level even after phosphorus is completely removed through struvite formation. In this study, both ammonia and phosphorus were recovered by adding leachate of sewage sludge ash (SSA) into ADPW. It was demonstrated that 11,600 mg L-1 of total phosphorus and 7266.7 mg L-1 of [Formula: see text]-P were extracted from SSA by using sulfuric acid at the H2SO4/SSA mass ratio of 0.35. ADPW and the leachate of SSA were mixed at the volumetric ratio of 1:1.29, and then struvite was formed at the molar ratio of 1.2 (Mg2+):1.0 ([Formula: see text]-P):1.0 (NH3-N). Removal efficiencies of ammonia and phosphorus were 91.95% and 99.65%, respectively. The obtained struvite was analyzed by various methods and was found to meet the Korean fertilizer standards, except for copper.

Long-term anaerobic digestion of food waste stabilized by trace elements.

The purpose of this study was to examine if long-term anaerobic digestion of food waste in a semi-continuous single-stage reactor could be stabilized by supplementing trace elements. Contrary to the failure of anaerobic digestion of food waste alone, stable anaerobic digestion of food waste was achieved for 368 days by supplementing trace elements. Under the conditions of OLR (organic loading rates) of 2.19-6.64 g VS (volatile solid)/L day and 20-30 days of HRT (hydraulic retention time), a high methane yield (352-450 mL CH(4)/g VS(added)) was obtained, and no significant accumulation of volatile fatty acids was observed. The subsequent investigation on effects of individual trace elements (Co, Fe, Mo and Ni) showed that iron was essential for maintaining stable methane production. These results proved that the food waste used in this study was deficient in trace elements.

Anaerobic co-digestion of food waste and piggery wastewater: focusing on the role of trace elements.

The objective of this study was to evaluate the feasibility of anaerobic co-digestion of food waste and piggery wastewater, and to identify the key factors governing the co-digestion performance. The analytical results indicated that the food waste contained higher energy potential and lower concentrations of trace elements than the piggery wastewater. Anaerobic co-digestion showed a significantly improved biogas productivity and process stability. The results of co-digestion of the food waste with the different fractions of the piggery wastewater suggested that trace element might be the reason for enhancing the co-digestion performance. By supplementing the trace elements, a long-term anaerobic digestion of the food waste only resulted in a high methane yield of 0.396 m(3)/kg VS(added) and 75.6% of VS destruction with no significant volatile fatty acid accumulation. These results suggested that the typical Korean food waste was deficient with some trace elements required for anaerobic digestion.