###### Abstract
It is also constrained downstream by costly and inefficient harvesting, cell disruption, product extraction, thermochemical conversion, hydrotreatment, and upgrading. A novel two-stage cultivation process was previously proposed to address various challenges of mass microalgal cultivation for biofuels and co-products and demonstrated using an oleaginous, haloalkaline-tolerant, and multi-trophic green _Chlorella_ sp. ALP2 isolated from a soda lake [1]. This involved cultivating the microalgae in a fermenter heterotrophically or photobioreactor mixotrophically on organic carbon (first-stage) to rapidly obtain high cell densities and inoculate an open-pondotrophic culture (second-stage) featuring high levels of NaHCO\({}_{3}\), pH, and salinity. The combination of high cell densities and extreme haloalkaline conditions in the second phototrophic stage could then minimize residence time and limit contamination [2], facilitate auto-flocculation harvesting [3], efficiently supply inorganic carbon [4], and enhance neutral lipid accumulation [5]. This two-stage process can be further improved upon with sustainable supplies of organic carbon for the first stage and nitrogen and phosphorous nutrients for the second stage. Organic carbon for the first-stage enclosed microalgal cultures can be derived from hydrolysates and/or condensates from processed ligno-cellulosic agricultural and/or forestry wastes. For instance, a glucose-containing enzymatic hydrolysate from high-temperature ethanol-treated rice-straw and an acetic acid-containing condensate from fast-pyrolyzed softwood were previously used to cultivate the microalgae _Chlorella pyrenoidosis_[6] and _Chlamydomonas reinhardtii_, respectively [7]. Hydrolysates from treated ligno-cellulosic biomass are advantageous over those resulting from starch and juice of agricultural crops such as Jerusalem artichoke, cassava, and sugarcane [6]. Namely, they contain both C\({}_{6}\) and C\({}_{5}\) sugars, avoid the \"food vs. fuel\" controversy, and are more cost-effective and higher-yielding than purchased glucose, which, in turn, was previously shown to be the highest-yielding carbon substrate for the _Chlorella vulgaris_ ALP2 microalgae, particularly under mixotrophic conditions [1]. Alternatively, condensates from thermochemically processing lignocellulosic biomass, i.e., fast-pyrolysis, represent a way of removing the carboxylic acids and levoglucan used for microalgal [7] and yeast cultivation [8] while simultaneously stabilizing pH, reducing corrosivity, and increasing heating-value of an intended bio-oil intermediary product that is later refined to fuel (i.e., green gasoline) or other chemicals. Despite these improvements, the conventional dilute sulfuric acid approach for hydrolysates and the fast-pyrolysis approach for condensates both have limitations. First, they require relatively expensive capital equipment for high-temperature and/or high-pressure operating conditions [9]. Second, such extreme conditions result in high levels of compounds in the hydrolysate and/or condensate that may inhibit microalgal growth [10]. Third, they fail to adequately address major logistical challenges and high costs (i.e., 30% of feedstock costs) associated with initially harvesting, transporting, storing, and grinding waste ligno-cellulosic biomass feedstock to uniform particle size for greater process efficiency prior to pre-treatment at a biorefinery [11]. Fourth, the selected lignocellulosic biomass may not be the most suitable. For instance, pyrolyzed forestry residues (i.e., softwood and hardwood) will yield less acetic acid and be less available, particularly during dark and cold winters when either indoor microalgal hetero-/mixotrophic cultivation or firewood combustion are implemented, compared to the very abundant, grassy agricultural crop residues (i.e., wheat-straw) after fall harvests [12,13]. Such by-products comprised up to 50% by weight of the world's 2 billion t year\({}^{-1}\) cereal crop production in 2011 [6].