Role of sufficient phosphorus in biodiesel production from diatom Phaeodactylum tricornutum.

In order to study the role of sufficient phosphorus (P) in biodiesel production by microalgae, Phaeodactylum tricornutum were cultivated in six different media treatments with combination of nitrogen (N) sufficiency/deprivation and phosphorus sufficiency/limitation/deprivation. Profiles of N and P, biomass, and fatty acids (FAs) content and compositions were measured during a 7-day cultivation period. The results showed that the FA content in microalgae biomass was promoted by P deprivation. However, statistical analysis showed that FA productivity had no significant difference (p = 0.63, >0.05) under the treatments of N deprivation with P sufficiency (N-P) and N deprivation with P deprivation (N-P-), indicating P sufficiency in N deprivation medium has little effect on increasing biodiesel productivity from P. triornutum. It was also found that the P absorption in N-P medium was 1.41 times higher than that in N sufficiency and P sufficiency (NP) medium. N deprivation with P limitation (N-P-l) was the optimal treatment for producing biodiesel from P. triornutum because of both the highest FA productivity and good biodiesel quality.

Biological phosphorus removal from abattoir wastewater at very short sludge ages mediated by novel PAO clade Comamonadaceae.

Recent increases in global phosphorus costs, together with the need to remove phosphorus from wastewater to comply with water discharge regulations, make phosphorus recovery from wastewater economically and environmentally attractive. Biological phosphorus (Bio-P) removal process can effectively capture the phosphorus from wastewater and concentrate it in a form that is easily amendable for recovery in contrast to traditional (chemical) phosphorus removal processes. However, Bio-P removal processes have historically been operated at medium to long solids retention times (SRTs, 10-20 days typically), which inherently increases the energy consumption while reducing the recoverable carbon fraction and hence makes it incompatible with the drive towards energy self-sufficient wastewater treatment plants. In this study, a novel high-rate Bio-P removal process has been developed as an energy efficient alternative for phosphorus removal from wastewater through operation at an SRT of less than 4 days. The process was most effective at an SRT of 2-2.5 days, achieving >90% phosphate removal. Further reducing the SRT to 1.7 days resulted in a loss of Bio-P activity. 16S pyrotag sequencing showed the community changed considerably with changes in the SRT, but that Comamonadaceae was consistently abundant when the Bio-P activity was evident. FISH analysis combined with DAPI staining confirmed that bacterial cells of Comamonadaceae arranged in tetrads contained polyphosphate, identifying them as the key polyphosphate accumulating organisms at these low SRT conditions. Overall, this paper demonstrates a novel, high-rate phosphorus removal process that can be effectively integrated with short SRT, energy-efficient carbon removal and recovery processes.

Operating aerobic wastewater treatment at very short sludge ages enables treatment and energy recovery through anaerobic sludge digestion.

Conventional abattoir wastewater treatment processes for carbon and nutrient removal are typically designed and operated with a long sludge retention time (SRT) of 10-20 days, with a relatively high energy demand and physical footprint. The process also generates a considerable amount of waste activated sludge that is not easily degradable due to the long SRT. In this study, an innovative high-rate sequencing batch reactor (SBR) based wastewater treatment process with short SRT and hydraulic retention time (HRT) is developed and characterised. The high-rate SBR process was shown to be most effective with SRT of 2-3 days and HRT of 0.5-1 day, achieving >80% reduction in chemical oxygen demand (COD) and phosphorus and approximately 55% nitrogen removal. A majority of carbon removal (70-80%) was achieved by biomass assimilation and/or accumulation, rather than oxidation. Anaerobic degradability of the sludge generated in the high-rate SBR process was strongly linked to SRT, with measured degradability extent being 85% (2 days SRT), 73% (3 days), and 63% (4 days), but it was not influenced by digestion temperature. However, the rate of degradation for 3 and 4 days SRT sludge was increased by 45% at thermophilic conditions compared to mesophilic conditions. Overall, the treatment process provides a very compact and energy efficient treatment option for highly degradable wastewaters such as meat and food processing, with a substantial space reduction by using smaller reactors and a considerable net energy output through the reduced aerobic oxidation and concurrent increased methane production potential through the efficient sludge digestion.